SEARCH · PubMed Health

Results for “VARIATION”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources

PubMed2005

Contribution of transcriptional regulation to natural variations in Arabidopsis.

BACKGROUND: Genetic control of gene transcription is a key component in genome evolution. To understand the transcriptional basis of natural variation, we have studied genome-wide variations in transcription and characterized the genetic variations in regulatory elements among Arabidopsis accessions. RESULTS: Among five accessions (Col-0, C24, Ler, WS-2, and NO-0) 7,508 probe sets with no detectable genomic sequence variations were identified on the basis of the comparative genomic hybridization to the Arabidopsis GeneChip microarray, and used for accession-specific transcriptome analysis. Two-way ANOVA analysis has identified 60 genes whose mRNA levels differed in different accession backgrounds in an organ-dependent manner. Most of these genes were involved in stress responses and late stages of plant development, such as seed development. Correlation analysis of expression patterns of these 7,508 genes between pairs of accessions identified a group of 65 highly plastic genes with distinct expression patterns in each accession. CONCLUSION: Genes that show substantial genetic variation in mRNA level are those with functions in signal transduction, transcription and stress response, suggesting the existence of variations in the regulatory mechanisms for these genes among different accessions. This is in contrast to those genes with significant polymorphisms in the coding regions identified by genomic hybridization, which include genes encoding transposon-related proteins, kinases and disease-resistance proteins. While relatively fewer sequence variations were detected on average in the coding regions of these genes, a number of differences were identified from the upstream regions, several of which alter potential cis-regulatory elements. Our results suggest that nucleotide polymorphisms in regulatory elements of genes encoding controlling factors could be primary targets of natural selection and a driving force behind the evolution of Arabidopsis accessions.

Arabidopsis↗

PubMed1998

Variation in measurements of range of motion: a study in reflex sympathetic dystrophy patients.

OBJECTIVE: To quantify the amount of variation attributed to different sources of variation in measurement results of upper extremity range of motion, and to estimate the smallest detectable difference (SDD) between measurements in reflex sympathetic dystrophy (RSD) patients. DESIGN: Two observers each measured in two sessions the range of motion of several upper extremity joints of RSD patients participating in an outcome study. SETTING: Department of Rehabilitation of a university hospital. SUBJECTS: Twenty-nine upper extremity RSD patients. MAIN OUTCOME MEASURES: The range of motion of forward flexion and external rotation of the shoulder, extension, flexion and supination of the elbow, palmar, dorsiflexion and ulnar, radial deviation of the wrist of affected and nonaffected sides, using a two-armed goniometer and an inclinometer. The measurement results were analysed using an analysis of variance according to the generalizability theory. RESULTS: The results indicate that observer and patient-observer were important sources of variation. The random error was the most important source of variation. Averaged over all ranges of motion the observer contributed 3.9% to the total variation, patient-observer interactions contributed 5.2% and the random error 20.3%. The SDD was smallest for elbow flexion, 7.1 degrees and 9.6 degrees and was largest for external rotation of the shoulder, 24.8 degrees and 28.7 degrees. The SDD was smaller for the nonaffected side as compared to the affected side for the majority of ranges of motion except elbow extension, wrist dorsiflexion, and radial and ulnar deviation. CONCLUSION: Clinically, our results indicate that range-of-motion measurements in RSD patients are subject to considerable variation and indicate that results of medical examinations in order to assess disability on the basis of range-of-motion measurements are subject to the same variation.

Arm↗

PubMed2004

Nucleotide variation of seven genes in Drosophila kikkawai.

We examined levels and patterns of nucleotide variation in 21 strains of Drosophila kikkawai from Miyako island, Japan for the partial regions of the following seven nuclear genes: Adh, Ddc, esc, ksr, Pgi, su(f), and Tpi. The nucleotide variation at total sites (pi(t)) ranged from 0.0013 in the ksr, to 0.0173 in the Adh. The nucleotide divergence at total sites (K(t)) between D. kikkawai and D. lini ranged from 0.0286 in the Tpi to 0.0687 in the su(f). The levels of nucleotide polymorphism and divergence were heterogeneous among the investigated gene regions. The HKA test, which tests imbalance between the intra and interspecific nucleotide variation, showed that the intraspecific nucleotide variation in the Pgi region was much lower than the interspecific variation, while intraspecific variation in the Tpi region was only slightly lower than interspecific variation. The MK test showed an excess of low frequency replacement polymorphic changes in the Adh region, suggesting that most replacement mutations are deleterious. Fay and Wu's test detected an excess of newly arisen variants in the Ddc region. In total, four of the seven gene regions showed significant deviation from the neutrality.

Alcohol Dehydrogenase↗

PubMed1990

Immunoreactive plasma cholinesterase (EC 3.1.1.8) substance concentration, compared with cholinesterase activity concentration and albumin: inter- and intra-individual variations in a healthy population group.

Substance concentrations of plasma cholinesterase (EC 3.1.1.8) were measured in 94 healthy individuals without occupational exposure to known inhibitors (six samples from each individual). Immunoreactive cholinesterase substance concentrations showed an inter-individual variation corresponding to CVtotal = 22% (mean: 5.01 mg/l, SD: 1.11 mg/l). Intra-individual variations of immunoreactive cholinesterase substance concentration were correlated (r = 0.36) to intra-individual variation of albumin. Estimated by a repeated-measures analysis of variance, the observed intra-individual variation of cholinesterase substance concentration corresponded to CV = 8.8% (SD: 0.44 mg/l), which together with a CVerror = 6% (within and between runs), implies a biological intra-individual variation of cholinesterase substance concentration corresponding to CVintra = 6.4%. Specific catalytic activity (kU/mg immunoreactive cholinesterase) was influenced by the ChE-1 phenotype (phenotype U: 1.58 kU/mg, phenotype UA: 1.22 kU/mg), but not by body weight, height, age, and sex. Observed intra-individual variation of specific catalytic activity corresponded to 6.4% (SD: 0.10 kU/mg), which together with an estimated CVerror = 6.2% implies the biological intra-individual variations of specific catalytic cholinesterase activity to be insignificant. The insignificant CVintra makes specific catalytic cholinesterase activity a rational quantity for evaluation of unexpected fluctuations of cholinesterase activity concentrations.

Adult↗

PubMed2004

Variation after a selective sweep in a subdivided population.

The effect of genetic hitchhiking on neutral variation is analyzed in subdivided populations with differentiated demes. After fixation of a favorable mutation, the consequences on particular subpopulations can be radically different. In the subpopulation where the mutation first appeared by mutation, variation at linked neutral loci is expected to be reduced, as predicted by the classical theory. However, the effect in the other subpopulations, where the mutation is introduced by migration, can be the opposite. This effect depends on the level of genetic differentiation of the subpopulations, the selective advantage of the mutation, the recombination frequency, and the population size, as stated by analytical derivations and computer simulations. The characteristic outcomes of the effect are three. First, the genomic region of reduced variation around the selected locus is smaller than that predicted in a panmictic population. Second, for more distant neutral loci, the amount of variation increases over the level they had before the hitchhiking event. Third, for these loci, the spectrum of gene frequencies is dominated by an excess of alleles at intermediate frequencies when compared with the neutral theory. At these loci, hitchhiking works like a system that takes variation from the between-subpopulation component and introduces it into the subpopulations. The mechanism can also operate in other systems in which the genetic variation is distributed in clusters with limited exchange of variation, such as chromosome arrangements or genomic regions closely linked to targets of balancing selection.

Animals↗

PubMed2005

Cryptic genetic variation is enriched for potential adaptations.

Cryptic genetic variation accumulates under weakened selection and has been proposed as a source of evolutionary innovations. Weakened selection may, however, also lead to the accumulation of strongly deleterious or lethal alleles, swamping the effect of any potentially adaptive alleles when they are revealed. Here I model variation that is partially shielded from selection, assuming that unconditionally deleterious variation is more strongly deleterious than variation that is potentially adaptive in a future environment. I find that cryptic genetic variation can be substantially enriched for potential adaptations under a broad range of realistic parameter values, including those applicable to alternative splices and readthrough products generated by the yeast prion [PSI+]. This enrichment is dramatically stronger when multiple simultaneous changes are required to generate a potentially adaptive phenotype. Cryptic genetic variation is likely to be an effective source of useful adaptations at a time of environmental change, relative to an equivalent source of variation that has not spent time in a hidden state.

Adaptation, Physiological↗

PubMed2006

Genetic variation in Drosophila melanogaster resistance to infection: a comparison across bacteria.

Insects use a generalized immune response to combat bacterial infection. We have previously noted that natural populations of D. melanogaster harbor substantial genetic variation for antibacterial immunocompetence and that much of this variation can be mapped to genes that are known to play direct roles in immunity. It was not known, however, whether the phenotypic effects of variation in these genes are general across the range of potentially infectious bacteria. To address this question, we have reinfected the same set of D. melanogaster lines with Serratia marcescens, the bacterium used in the previous study, and with three additional bacteria that were isolated from the hemolymph of wild-caught D. melanogaster. Two of the new bacteria, Enterococcus faecalis and Lactococcus lactis, are gram positive. The third, Providencia burhodogranaria, is gram negative like S. marcescens. Drosophila genotypes vary highly significantly in bacterial load sustained after infection with each of the four bacteria, but mean loads are largely uncorrelated across bacteria. We have tested statistical associations between immunity phenotypes and nucleotide polymorphism in 21 candidate immunity genes. We find that molecular variation in some genes, such as Tehao, contributes to phenotypic variation in the suppression of only a subset of the pathogens. Variation in SR-CII and 18-wheeler, however, has effects that are more general. Although markers in SR-CII and 18-wheeler explain >20% of the phenotypic variation in resistance to L. lactis and E. faecalis, respectively, most of the molecular polymorphisms tested explain <10% of the total variance in bacterial load sustained after infection.

Animals↗

PubMed2005

Genetic variations and haplotypes of CYP2C19 in a Japanese population.

Forty-eight single nucleotide variations, including 27 novel ones, were found in the 5'- regulatory region, all of the exons and their surrounding introns of CYP2C19 in 253 Japanese subjects (134 diabetic patients and 119 healthy volunteers). Identified novel variations were as follows: -2772G>A, 2767_-2760delGGTGAACA, -2720T>C, -2547delG, -2545G>T, -2545_-2544 delGC, and -2040C>T in the enhancer region; -778C>T, -777G>A, -529G>C, -189C>A, and -185A>G in the promoter region; 151A>G (S51G), 481G>C (A161P), 986G>A (R329H), 1078G>A (D360N), and 1119C>T (D373D) in the exons, and IVS1+128T>A, IVS3+163G>A, IVS4+271A>G, IVS5-49A>G, IVS6-210C>T, IVS6-196T>A, IVS6-32T>A, IVS7+84G>A, IVS7-174C>T, and IVS8+64C>T in the introns. Since we found no significant differences in the variation frequencies between healthy volunteers and diabetic patients, the data for all subjects were treated as one group in further analysis. The allele frequencies were 0.265 for IVS6-196T>A, 0.045 for -2772G>A and -2720T>C, 0.024 for -2040C>T, 0.014 for IVS7-174C>T, 0.010 for -529G>C, 0.006 for IVS1+128T>A and 481G>C (A161P), 0.004 for -2767_-2760delGGTGAACA and IVS6-210C>T, and 0.002 for the other 17 variations. In addition, the two known nonsynonymous single nucleotide polymorphisms, 681G>A (splicing defect, (*)2 allele) and 636G>A (W212X; (*)3 allele) were detected at 0.267 and 0.128 frequencies, respectively. No variation was detected in the known binding sites for constitutive androstane receptor and glucocorticoid receptor. Linkage disequilibrium analysis showed several close linkages of variations throughout the gene. By using the variations, thirty-one haplotypes of CYP2C19 and their frequencies were estimated. Our results would provide fundamental and useful information for genotyping CYP2C19 in the Japanese and probably other Asian populations.

Aryl Hydrocarbon Hydroxylases↗

PubMed1993

Diagnosis of meniscal tears of the knee with MR imaging: effect of observer variation and sample size on sensitivity and specificity.

OBJECTIVE: A wide range in the efficacy of MR imaging for the diagnosis of meniscal tears of the knee has been reported. To evaluate two possible causes for this variation, we studied how sensitivity and specificity are affected when different observers and sample sizes are used. MATERIALS AND METHODS: Two hundred MR examinations of the knee in patients for whom the results of arthroscopy were available were used for the study. One hundred eight medial meniscal tears and 58 lateral meniscal tears were found at arthroscopy. The sensitivity and specificity for detection of meniscal tears were determined for the original interpretations and retrospective evaluations by three observers. Comparisons were also made between sample sizes of 25 and 100. chi 2 analysis was used for unmatched data sets and McNemar's statistic was used for matched sets. RESULTS: For the 200 examinations, the sensitivity was 0.89-0.93 for medial meniscal tears and 0.79-0.83 for lateral meniscal tears. The specificity was 0.86 for medial meniscal tears and 0.90-0.92 for lateral meniscal tears. Sensitivity and specificity varied widely among different observers and different sample sizes. However, we found no significant difference between any of the comparisons at the p < .05 level. The largest interobserver variation occurred in the detection of lateral meniscal tears, with a sensitivity of 0.71 for one observer and 0.88 for another observer (p = .16). The largest variation between sets of 100 examinations was a change in sensitivity for detection of lateral meniscal tears from 0.74 to 0.88 for the original interpretations (p = .10). For the sample sets of 25 cases, the variation was even larger, with the sensitivity for detection of lateral meniscal tears varying from 0.5 for one set to 1.0 for another. CONCLUSION: We conclude that chance variation related to sample size can cause large but not statistically significant variations in sensitivity and specificity in this setting. These variations are of sufficient magnitude to explain many of the differences in reported sensitivity and specificity for MR imaging in the diagnosis of meniscal tears. We found no significant difference in observer performance.

Adolescent↗

PubMed1994

Genetic variation of broiler feed consumption and efficiency corrected for differences in test body weights.

Feed consumption and feed efficiency data obtained over nine generations from three selected strains of broilers were adjusted for differences in either initial or initial and final test BW (at 28 and 42 d, respectively). Genetic and environmental variables were estimated for each strain using an animal model with restricted maximum likelihood procedures to avoid bias due to reduced genetic variation caused by selection. Variance component and heritability estimates before and after adjustment of these traits for differences in test weights were evaluated. Adjustments of feed consumption data for either initial test BW or both initial and final test BW reduced additive genetic and environmental variation. Reductions were relatively greater for additive genetic than for environmental variance, thereby reducing the heritability of the adjusted trait. Adjustment of feed efficiency for initial test BW altered additive genetic variation little and reduced environmental variation slightly; however, correction for both test BW reduced variation of both components. Heritability of adjusted feed efficiency was 40% larger (.33 to .35 vs .21 to .28) than for uncorrected feed efficiency, but phenotypic variation of the adjusted feed efficiency was reduced 42% (5.82 to 6.13 vs 10.30 to 11.35). Heritabilities of feed consumption and efficiency were essentially the same (.34 and .36) after adjustment for both test weights. Changes in genetic and environmental variation and heritability due to adjustments were similar for the three strains.

Animals↗

PubMed1999

Inter-patient and intra-patient variations in the baseline tapping test in patients with Parkinson's disease.

Inter-patient and intra-patient variations in the baseline values of the tapping test were studied in 22 patients with Parkinson's disease using the unequal sample sizes model II one-way analysis of variance (ANOVA). The results show that intra-patient variation accounts for about 15.8% of the total variation, inter-patient variation accounts for about 84.2% of the total variation, and the coefficient of variation (CV) in intra-patient variation is 15.8%. The results suggest that at least two or three baseline tapping tests are needed to determine the baseline value of the tapping test.

Aged↗

PubMed1996

Genomic variation in C. albicans.

Candida albicans displays many types of variation which affect a broad spectrum of phenotypes. Among them are antigenic, chromosomal, morphologic, and biochemical variation. The ability to modulate many phenotypes is clearly an important factor in the success of this fungus as a pathogen and variation at the genomic level may be the common denominator among the different systems. Genomic variation in C. albicans has been studied by many researchers and a number of different mechanisms have been identified. Among them are ploidy fluctuations, which allow the organism to cycle from 2n chromosome number to 4n or higher; translocation, which has been demonstrated to involve many different chromosomes and affects many phenotypes including virulence; mitotic recombination, which has been demonstrated to increase resistance to certain drugs; and nondisjunction, which has been shown to have morphological consequences. The number and diversity of these mechanisms combine to make C. albicans a highly successful organism. Although normally a commensal of humans, when invasive, C. albicans can inhabit almost any site in the body. It is not known what governs the transition of C. albicans from a commensal to pathogenic invader, however, variation at the genomic level likely plays a role. One possible consequence of variation is the generation of atypical strains, further expanding the documented phenotypic plasticity of this organism. The exposure of patients to cytotoxic drugs during treatment of such diseases as AIDS or cancer increases the selective pressure and has exacerbated both the frequency and degree of variability observed in C. albicans. The molecular analysis of genomic variation in C. albicans is proving to be a fertile area of research and future investigations can only be expected to add to the mechanisms documented in this review.

Candida albicans↗

PubMed2004

Seasonal variation in serum cholesterol levels: treatment implications and possible mechanisms.

BACKGROUND: A variety of studies have noted seasonal variation in blood lipid levels. Although the mechanism for this phenomenon is not clear, such variation could result in larger numbers of people being diagnosed as having hypercholesterolemia during the winter. METHODS: We conducted a longitudinal study of seasonal variation in lipid levels in 517 healthy volunteers from a health maintenance organization serving central Massachusetts. Data collected during a 12-month period for each individual included baseline demographics and quarterly anthropometric, blood lipid, dietary, physical activity, light exposure, and behavioral information. Data were analyzed using sinusoidal regression modeling techniques. RESULTS: The average total cholesterol level was 222 mg/dL (5.75 mmol/L) in men and 213 mg/dL (5.52 mmol/L) in women. Amplitude of seasonal variation was 3.9 mg/dL (0.10 mmol/L) in men, with a peak in December, and 5.4 mg/dL (0.14 mmol/L) in women, with a peak in January. Seasonal amplitude was greater in hypercholesterolemic participants. Seasonal changes in plasma volume explained a substantial proportion of the observed variation. Overall, 22% more participants had total cholesterol levels of 240 mg/dL or greater (> or =6.22 mmol/L) in the winter than in the summer. CONCLUSIONS: This study confirms seasonal variation in blood lipid levels and suggests greater amplitude in seasonal variability in women and hypercholesterolemic individuals, with changes in plasma volume accounting for much of the variation. A relative plasma hypervolemia during the summer seems to be linked to increases in temperature and/or physical activity. These findings have implications for lipid screening guidelines. Further research is needed to better understand the effects of a relative winter hemoconcentration.

Adult↗

PubMed2001

Intraindividual variation of prostate specific antigen measurement and implications for early detection of prostate carcinoma.

BACKGROUND: Many researchers have described intraindividual prostate specific antigen (PSA) variation, but its implications for a prostate carcinoma screening program have not been well appreciated. In this study, the author explored misclassification problems associated with intraindividual PSA variation. METHODS: The previous research work on intraindividual PSA variation was reviewed and summarized. Then, on the basis of the results from the previous work and a simple measurement error model, the author estimated misclassification probabilities for a single PSA measurement. RESULTS: With a variance-based approach of meta-analysis, the author derived a summary coefficient of variation (13.1%) of the intraindividual PSA variation from the previous relevant studies. They found that there were substantial risks for misclassification, especially among those with PSA values near the recommended cutoff point (4.0 ng/mL). For an individual with a true PSA level at 3.9 ng/mL, the risk for misclassification as PSA higher than 4.0 ng/mL was approximately 42%; for an individual with a true PSA value at 3.0 ng/mL, the risk was less than 1%. CONCLUSIONS: Intraindividual PSA variation should become a part of interpreting PSA test results, especially for men with a PSA value near the cutoff point. Both sensitivity and specificity of PSA test reported in the literature have been underestimated, and the risk of prostate carcinoma associated with PSA test results has been biased down to the null (no effect) because of the intraindividual PSA variation.

Humans↗

PubMed1980

Variation in the baseline sister chromatid exchange frequency in human lymphocytes.

The utility of the sister chromatid exchange (SCE) assay for human population studies is potentially limited by the variability associated with individual baseline SCE Frequencies. This investigation identifies and quantifies the major sources of preparative and biological variation associated with the determination of baseline SCE frequencies in cultured human lymphocytes. Much of the variation in lymphocyte SCE frequencies is attributable to the amount of bromodeoxyuridine (BrdUrd) available per lymphocyte; the pooled coefficient of variation (CV) over the dose range of 10 to 160 micrometer is about 18%. Other variations in the baseline frequency result from culture-to-culture and slide-to-slide differences. The pooled coefficient of variation among donors is about 10%. The effect of cell-to-cell differences in baseline SCE frequency among donors can be minimized by increasing the number of cells scored per donor. When 20 cells are analyzed per individual the pooled cell-to-cell variation is 9% but when 40 or 80 cells are analyzed it is reduced to 6 and 4% respectively. For a single individual the cell-to-cell coefficient of variation at 100 micrometer BrdUrd is 40.8%. Under our experimental conditions, a 30% increase in SCE frequency between two cohort populations can be detected with a 95% probability at a 5% level of significance when 11 individuals per cohort are studied. For a longitudinal or in vitro dose response study of a single individual, a 50% increase in SCE frequency can be detected with a 95% probability at a 5% level of significance when 25 cells per sample are analyzed. These results indicate the feasibility of applying the SCE bioassay to humans as a measure of environmental stress.

Biological Assay↗

PubMedDate not supplied

Does nifedipine affect the diurnal variation of asthma in children?

Diurnal variations in airway caliber and in bronchial reactivity have been described. The mechanisms underlying these variations are not known. The hypothesis that these variations can be diminished by calcium channel blockers was tested by giving 22 asthmatic children 10 mg of nifedipine or identical placebo three times a day for 4 weeks in a double-blind, randomized, crossover-designed study. Treatment with nifedipine did not diminish the diurnal variations in airway caliber, judged from peak expiratory flow rates, or in bronchial reactivity, judged from bronchodilator responsiveness. Group mean amplitude of the diurnal variation in airway caliber was 10.5% on nifedipine and 10.6% on placebo. Group mean amplitude of the diurnal variation in bronchodilator responsiveness was 75.4% on nifedipine and 69.5% on placebo. There were no differences in mean peak expiratory flow rate between nifedipine and placebo periods. This study did not find any evidence to support the hypothesis that the diurnal variations in airway caliber and in bronchial reactivity can be diminished by calcium channel blockers.

Adolescent↗

PubMed1998

A simulation test of hominoid species number at Lufeng, China: implications for the use of the coefficient of variation in paleotaxonomy.

High dental metric variation in the large hominoid sample from the late Miocene site of Lufeng, China has been interpreted in two ways: (1) there are two morphologically similar species that broadly overlap in size, and (2) there is one species that is more highly sexually dimorphic in dental size, and perhaps in body size, than any extant primate. It has been claimed that the high levels of dental metric variation falsify the single-species hypothesis, which has been viewed implicitly as corroboration of the two-species hypothesis. However, the two-species hypothesis has not been subjected to testing. Here we test the two-species hypothesis using computer simulations to attempt to reproduce the unusual pattern of intrasexual and intersexual dental metric variation observed in the Lufeng postcanine dentition. Conditions of the simulation experiments were optimized to favor the two-species hypothesis. It was found that, although the Lufeng pattern of metric variation could be reproduced by sampling two species, the likelihood of this occurrence was very low even when the conditions were optimized to the point of improbability. We conclude that the likelihood is very high that the Lufeng sample is composed of one species that is more highly sexually dimorphic in the postcanine dentition than any extent primate species. If so, then the high levels of sexual dimorphism and intraspecific dental metric variation in this species violate the central assumption of methods that employ the coefficient of variation (CV) for paleotaxonomy, namely, that neither can lie outside the ranges observed among extant species. Thus, we further conclude that the CV must be used with caution when evaluating the taxonomic composition of fossil samples and, further, that it cannot be used to falsify a single-species hypothesis in any meaningful way. Other fossil hominoid samples with high measures of dental variation may indicate that considerable sexual size dimorphism typified many Eurasian middle-late Miocene hominoids.

Animals↗

PubMed1993

Variation in concentrations of RNAs and proteins involved in gene expression of Escherichia coli.

A growing cell is not a steady-state situation. At some point in the cell cycle each gene doubles its concentration, which may result in a doubling of the production rate of its mRNA. The variations in concentration of mRNAs and proteins in an individual exponentially growing cell are studied for a gene which is constitutive, autorepressed, or autoactivated. Analysis of the mathematical model for a constitutive gene shows a fixed variation in concentration of a stable RNA between its minimum and maximum concentration of approximately 6%, independent of cell cycle time or gene location. The variation in the concentrations of the mRNA and protein for a constitutive gene are studied as gene position, molecular stability, and cell cycle time are varied. One result shows that doubling the growth rate can more than double the percentage of product from a gene near the origin of replication compared to one near the terminus. Results from these theoretical studies compare favorably to experimental results for rRNAs and the fully induced lac gene. Additional studies were performed to determine the effects of autorepression and autoactivation on the variation of concentration of mRNAs and proteins. The studies show that RNA and protein products of an autorepressed gene have almost the same variation in concentration as products of a constitutively expressed gene though the absolute concentrations are decreased. It is shown that the stability of an mRNA or protein affects variation in its concentration throughout the cell cycle, much more than the type of genetic control. The strength of repression has no effect on the variation in concentration of RNA and protein gene products through a cell cycle. Studies of an autoactivated gene show that it is significantly more responsive to a shift up or down, such as those caused by nutritional changes. An example is provided where the autoactivated gene is not expressed at one growth rate, but turns on at a higher growth rate. Furthermore, it is shown that gene position may determine whether or not the autoactivated gene is expressed.

Bacterial Proteins↗