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Results for “phase variation”

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PubMed1975

Cell-envelope proteins of Bordetella pertussis.

Cell-envelope polypeptides of eight phase-I and five phase-IV strains of Bordetella pertussis were compared by SDS-polyacrylamide gel electrophoresis. All phase-I strains gave a strikingly similar but complex pattern of protein bands, which did not appear to vary with known differences in heat-labile agglutinogens. Phase-IV strains gave the same pattern as phase-I strains, except that one band was missing and another was either much reduced or absent. Envelopes from phase-I strains grown in Hornibrook medium rich in Mg-2+ ions to produce "antigenically-modulated" C-mode cells gave a pattern of bands indistinguishable from phase-IV strains. A phase-IV strain grown in the high-Mg-2+ medium gave the same pattern of bands as when grown in unmodified Hornibrook medium. We suggest that the two polypeptide bands that show changes may be responsible for one or more of the immunological or physiopathological activities that are lost during phase variation and antigenic modulation in B. pertussis.

Allergens↗

PubMed1992

Evidence for global regulatory control of pilus expression in Escherichia coli by Lrp and DNA methylation: model building based on analysis of pap.

Pyelonephritis-associated pilus (Pap) expression is regulated by a phase variation control mechanism involving PapB, Papl, catabolite activator protein (CAP), leucine-responsive regulatory protein (Lrp) and deoxyadenosine methylase (Dam). Lrp and Papl bind to a specific non-methylated pap regulatory DNA region containing the sequence 'GATC' and facilitate the formation of an active transcriptional complex. Evidence indicates that binding of Lrp and Papl to this region inhibits methylation of the GATC site by Dam. However, if this GATC site is first methylated by Dam, binding of Lrp and Papl is inhibited. These events lead to the formation of two different pap methylation states characteristic of active (ON) and inactive (OFF) pap transcription states. The fae (K88), daa (F1845) and sfa (S) pilus operons share conserved 'GATC-box' domains with pap and may be subject to a similar regulatory control mechanism involving Lrp and DNA methylation.

Bacterial Proteins↗

PubMed1977

Isolation and characterization of Escherichia coli phase variants and mutants deficient in type 1 pilus production.

Type 1 pili of Escherichia coli are the prototype of the somatic class of pili found on many strains of bacteria. As a first step in the genetic analysis of type 1 piliation, an extensive series of nonpiliated derivatives of E. coli K-12 strain AW405, was characterized to produce attached or free pili when examined in the antiserum or appeared to produce attached or free pili when examined in the electron microscope. The derivatives fell into two classes; phase variants and mutants. Phase variants that formed colonies of two distinctive types, one associated with a predominantly piliated (P+), and the other associated with a nonpiliated (P-) phase, were obtained. Each phase could give rise to the other at a relatively high rate, which was greater in the P- to P+ direction during culture in unshaken liquid medium. In addition, 77 Pil- mutants were selected on the basis of a subtle difference in colonial morphology. The mutants reverted, if at all, at a much lower rate than that of the P- to P+ change. The stability of Pil- derivatives grown in unshaken liquid medium was used as a criterion for distinguishing between phase variants and mutants, Phase variation also effected colonial morphology and chemotactic swarming. These properties did not directly depend upon piliation since Pil- mutants were only slightly altered in colonial form and unaltered in chemotactic swarming. Piliation of Pil+ bacteria was quantitatively affected by growth conditions.

Chemotaxis↗

PubMed1979

Serotyping of Serratia marcescens: current status of seven recently described flagellar (H) antigens.

The slightly revised, current scheme of 20 flagellar (H) antigens of Serratia marcesens was examined. The seven new H antigens were demonstrated to be antigenically distinct as determined with Le Minor's H-immobilization test. The H-immobilization antibodies of rabbit anti-H immune sera proved resistant to treatment with 2-mercaptoethanol and dithiothreitol, respectively. On the other hand, dual absorptions of rabbit anti-H immune sera with killed cells of Staphylococcus aureus strain Cowan I, i.e., protein A, failed to reduce significantly H-immobilization titers of rabbit sera, although human immunoglobulins G and M were bound by protein A. It was tentatively concluded that the 2-mercaptoethanol- and dithiothreitol-refractory H-immobilizing rabbit antibodies belonged to the immunoglublin M class. H-antigen (phase) variation was not demonstrable in several extramural, clinical isolates of S. marcescens for which this phenomenon had been claimed. Rather, four of these six isolates were found to consist of cell populations of two distinct serotypes, as also borne out by bacteriocin typing; the flagellar H-antigens of the remaining two isolates were stable, with minor, hterologous H-antigen cross-reactivity.

Antigens, Bacterial↗

PubMed1992

Role of fimbrial adhesins in the pathogenesis of Escherichia coli infections.

Escherichia coli strains are able to cause intestinal (enteritis, diarrhoeal diseases) and extraintestinal (urinary tract infections, sepsis, meningitis) infections. Most pathogenic E. coli strains produce specific fimbrial adhesins, which represent essential colonization factors: intestinal E. coli strains very often carry transferable plasmids with gene clusters specific for fimbrial adhesins, like K88 and K99, or colonization factor antigens (CFA) I and II. In contrast, the fimbrial gene clusters of extraintestinal E. coli strains, such as P, S, or F1C fimbriae, are located on the chromosomes. The fimbrial adhesin complexes consist of major and minor subunit proteins. Their binding specificity can generally be assayed in hemagglutination tests. In the case of fimbrial adhesins of intestinal E. coli strains, the major subunit proteins preferentially represent the hemagglutinating adhesins, whereas minor subunit proteins are the hemagglutinins of extraintestinal E. coli strains. Recently "alternative" adhesin proteins were identified, which have the capacity to bind to eukaryotic structures different from the receptors of the erythrocytes. Fimbrial adhesins are not constitutively expressed but are stringently regulated on the molecular level. Extraintestinal E. coli wild-type strains normally carry three or more fimbrial adhesin determinants, which have the capacity to influence the expression of one another (cross talk). Furthermore the fimbrial gene clusters undergo phase variation, which seems to be important for their contribution to pathogenesis of E. coli.

Animals↗

PubMed1977

Spatial frequency and light-spread descriptions of visual acuity and hyperacuity.

Resolution (visual acuity) and differential spatial localization (hyperacuity) targets were selected to allow rigorous psychophysical measurements as well as ready expression of both their spatial frequency spectrum and their retinal image light distribution. Thresholds were about 1 arc min for acuity and 4-6 arc sec for hyperacuity. As is consistent with the reciprocal relationship between the space and spatial frequency domains, the small locally restricted spatial differences between just distinguishable patterns are represented in the frequency domain by equally small differences, which are distributed over the entire spatial frequency spectrum. While they occur in many test situations, phase variations of spatial frequency components are not necessary for achieving optimum acuity and hyperacuity.

Female↗

PubMed1992

Molecular characterization of cloned variants of Coxiella burnetii isolated in China.

To study the molecular properties of Coxiella burnetii phase variants we cloned the phase variants of C. burnetii Qiyi (CBQY) strain by the red plaque technique. Three cloned strains, CBQYIC3 (phase I), CBQYIIC7 (phase II) and CBQYIIC5 (semirough-phase) were analysed by SDS-PAGE, immunoblot assay, plasmid isolation and agarose gel electrophoresis of DNA restriction fragments. The results suggest that the unique phase-dependent substance is a lipopolysaccharide and that most protein components of phase I and phase II cells are shared. No significant differences of DNA restriction fragments were found between clonal isolates of phase I and phase II C. burnetii CBQY strains. A plasmid of approximately 56 Kb was isolated from both phase I and phase II variants indicating that phase variation probably could not be attributed to its presence or absence.

Bacterial Proteins↗

PubMed1975

Phase II to phase I conversion of Coxiella burneti in immunosuppressed mice.

Coxiella burneti strains 48 and Nine Mile, serologically in phase II, changed their antigenic properties and virulence for guinea pigs and mice upon passaging in immunosuppressed mice. Conversion to phase I of these strains in a system lacking antibody response throws doubt on the importance of specific antibodies in phase variation of C. burneti.

Animals↗

PubMed1977

Creatine kinase: stability, inactivation, reactivation.

I determined the in vitro biological half-lives or decay constants for creatine kinase isoenzymes at various temperatures. Values at 37 degrees C are consistent with values reported by others in vivo, which suggests that in vivo irreversible inactivation is primarily thermal. Reversible inactivation appears to be an oxidation-reduction phenomenon. Proteins and some inactivators (urate, catecholamines) retard irreversible inactivation and preserve isoenzyme integrity. Dilution and thiols promote reversal of inactivity. Mercaptoethanol is the preferred thiol, particularly for storage and reactivation of isoenzyme MB. MB is sensitive to light and to freeze-thawing. I recommend that specimens be cooled promptly after drawing, that mercaptoethanol (10 mmol/liter) be added, and that they be stored refrigerated. Avoid prolonged exposure to light and freezing. A model of inactivation is proposed, which is based on the assumed existence of four monomer types: active, denatured, oxidized, and insulated. The model is consistent with dilution and thiol reactivation, lag phase variations, and subtype heterogeneity.

Catecholamines↗

PubMed1977

Effect of strain variation and growth phase of culture on dry weight and hexosamine content of cell wall layers of a marine pseudomonad.

Two variants of marine pseudomonad B-16 (ATCC 19855) differing in that one, variant 3, formed opaque colonies and the other, variant 7, formed translucent colonies were examined to determine if the variants differed in the amount and hexosamine content of their three outer cell wall layers. In both variants, the three outer layers of the cell wall, the loosely bound outer layer, the outer double-track layer, and the underlying (periplasmic space) layer contributed less to the dry weight of the cells when the cells were harvested in the stationary than in the logarithmic phase of growth. The hexosamine content of the layers of variant 3 increased dramatically as the cells went from the logarithmic to the stationary phase. The hexosamine content of the layers of variant 7 changed little by comparison. Thus cells of the variant which forms opaque colonies enrich the outer layers of their cell wall with hexosamine when grown to stationary phase.

Cell Wall↗

PubMed1979

Variation in S phase in synchronous human cell lines.

Growth parameters of diploid and trisomic human fibroblasts were determined. The rate of growth of both classes of cells was examined in asynchronous cultures, and diploid and trisomic cells had similar growth rates. Synchronous cultures were developed using simple mitotic selection. The patterns and length of the DNA synthetic period (S phase) were found to be altered in trisomy 21 cells when compared to diploid human or to heteroploid HeLa cells. Early S-phase synthesis was absent or reduced and the overall length of the S phase was extended. However, the trisomic cells have apparently normal rates of DNA chain elongation and normal replicon sizes.

Cell Cycle↗

PubMed1992

Circadian variations in cell cycle phase progression of mouse epidermal cells measured directly by bivariate BrdUrd/DNA flow cytometry.

Circadian stage-dependent variations in cell cycle traverse of mouse epidermal cells in vivo were investigated. The fate of cohorts of basal cells pulse-labelled with bromodeoxyuridine (BrdUrd) at different times of the day were studied by bivariate BrdUrd/DNA flow cytometry of isolated epidermal basal cells. Basal cells were tracked through the cell cycle up to 96 h after intraperitoneal injection of BrdUrd at 0800 and 2000, or followed for 6 h after BrdUrd injection at 0400, 1200, 1600 and 2400. The results confirmed our previous assumption that the cell cycle progression through S phase and G2 phase is considerably delayed at night, i.e. from 1600 to 0400, compared with daytime. The results indicate variations in G1 phase as well. The data strongly support the hypothesis that the main parameters responsible for circadian fluctuations in mitotic activity are variations in the S and G2 phase durations. The data are also consistent with the notion of proliferative heterogeneity among basal cells as described by a hierarchical proliferation model.

Animals↗

PubMed1979

Circadian rhythms in mouse epidermal basal cell proliferation. Variations in compartment size, flux and phase duration.

Several kinetic parameters of basal cell proliferation in hairless mouse epidermis were studied, and all parameters clearly showed circadian fluctuations during two successive 24 hr periods. Mitotic indices and the mitotic rate were studied in histological sections; the proportions of cells with S and G2 phase DNA content were measured by flow cytometry of isolated basal cells, and the [3H]TdR labelling indices and grain densities were determined by autoradiography in smears from basal cell suspensions. The influx and efflux of cells from each cell cycle phase were calculated from sinusoidal curves adapted to the cell kinetic findings and the phase durations were determined. A peak of cells in S phase was observed around midnight, and a cohort of partially synchronized cells passed from the S phase to the G2 phase and traversed the G2 phase and mitosis in the early morning. The fluctuations in the influx of cells into the S phase were small compared with the variations in efflux from the S phase and the flux through the subsequent cell cycle phases. The resulting delay in cell cycle traverse through S phase before midnight could well account for the accumulation of cells in S phase and, therefore, also the subsequent partial synchrony of cell cycle traverse through the G2 phase and mitosis. Circadian variations in the duration of the S phase, the G2 phase and mitosis were clearly demonstrated.

Animals↗

PubMed1976

Lunarperiodic variation of the phase-angle difference in nocturnal animals under natural Zeitgeber-conditions near the equator.

Several months' studies under natural illumination conditions in the vicinity of the equator show that night monkeys (Aotus trivirgatus), and leaf-nosed bats (Artibeus lituratus) exhibit species-specific lunarperiodic changes of the phase position of their activity rhythm to the Zeitgeber rhythm (Figures 1-3). These changes are closely to nightly illumination conditions. In Aotus the phase-angle differences (p.a.ds) of the onset and end of the activity phase, and in Artibeus the p.a.ds of the midpoint and end of the activity phase are significantly dependent upon the phases of the moon. In the African fruit bat Rousettus aegyptiacus, and in the leaf-nosed bat Phyllostomus hastatus no statistically significant lunarperiodic changes of the p.a.ds could be detected. These results cannot be explained by means of current models concerning the mechanism of synchronisation of biological oscillation. They appear to be, instead, expressions of a periodic masking of the real phase-position due to direct effects of light intensity on the level of activity which which itself is determined by the circadian rhythm. Aschoff's rule, which states that the earlier a species or an individual awakes the later it terminates its daily phase of activity, is partly confirmed for the nocturnal mammals examined in the present study.

Animals↗

PubMed1976

The concordance of respiratory fluctuations in oesophageal and central venous pressures.

Respiratory fluctuations in oesophageal and central venous pressures were recorded in 13 healthy subjects and compared with respect to phase and amplitude concordance. An average divergence in phase of nearly 180 degrees was obtained, with large inter-individual variations. Disregarding phase the amplitude of the respiratory central venous pressure was found to be, on the average, a good 1/4 of that of the oesophageal pressure in the supine posture, and a good 2/3 while the subjects were sitting. These figures also varied considerably. It is suggested that the findings might be referred to competition between a central venous pressure raising effect of inspiration enhanced venous return, and a central venous pressure depressing effect of the inspiratory fall in intrathoracic pressure. The partitioning of costal and abdomino-diaphragmatic breathing is considered of great significance to the outcome of this competition. It is concluded that the oesophageal balloon catheter technique for estimation of transpulmonary pressure cannot simply be replaced by the central venous catheter technique in healthy subjects. Its application in patients with certain pulmonary disorders, however, might be more successful.

Adult↗

PubMed1975

Rate and time of DNA synthesis of individual Chinese hamster cells.

The duration of DNA synthesis of a diploid cell line of Chinese hamster fibroblasts was determined in a comparative study by the FLM technique, and also by a new technique for measuring the rate of DNA synthesis of individual cells. These methods produced comparable results when applied during exponential growth of the cells. The rate of DNA synthesis was measured by means of quantitative autoradiography following a short-term incubation of the cells with 5 X 10(-6) M FUdR and 10(-5) M 14C-TdR. The choice of the medium for this purpose did not seem to be critical. The autoradiographic silver grains over cells and 14C-standard sources are counted by microphotometry using incident light bright-field. The direct measurements of DNA synthesis rate are 'compartment' statistics which have been converted into 'flux' parameters for comparison with the FLM method and applicability in cell-kinetic calculations. Frequency distributions of the rate of DNA synthesis of individual cells thus obtained may resemble normal distributions quite closely. They result from several factors: differences in the rate of synthesis in different parts of the S-phase, the density distribution of cells within the S-phase, the variation in the time of DNA synthesis among individual cells, and the experimental error. In the case of a pronounced partial synchronization as probably has been present in one experiment performed in the lag phase, an incorrect time of DNA synthesis may result from the rate values. Due to the variation in DNA synthesis rate in different parts of the S-phase it is not possible to determine the duration of DNA synthesis of an individual cell. However, the mean values of DNA synthesis time are reliable. The new method will be preferentially applied for determining the duration of DNA synthesis of human cells in as far as difficulties are encountered with the classical methods. In addition, it may be used to advantage for studying cells which make up low percentages in mixed populations. It finally permits a safer morphological classification of the cells under study than is possible with the classical methods.

Autoradiography↗

PubMed1975

Variations of neurohypophysial function in normally cycling women.

Using a neurophysin radioimmunoassay, we have studied basal neurohypophysial function in seven normal women. An increase in neurophysin blood levels has been demonstrated during the ovulatory and/or luteal phase as compared to the follicular phase; these variations are related to the changes in the circulating levels of 17beta-estradiol. The data provide additional evidence for a relationship between estrogens and neurohyprophysial function, as previously shown following exogenous administration of estriol and ethinyl estradiol in man.

Adult↗

PubMed1979

[Periodic modifications of the preoptico-terminal LRH tract in the squirrel monkey during the estrous cycle (author's transl)].

The quantities of specific immunoreactive material along the preoptico-terminal LRH tract show important modifications during the estrous cycle in the squirrel monkey. During the late follicular phase and the peri-ovulatory period the preoptico-terminal LRH tract shows "low" or "very low" fluorescence intensity. A progressive but very important increase occurs during the luteal phase, followed by great variations during the early and middle follicular phases. These variations suggest a conspicuous release of LRH, especially during the middle follicular phase. It is supposed that the preoptico-terminal LRH tract (whose LRH is released into the capillaries of the vascular organ of the lamina terminalis and reaches the systemic blood) controls gonadotropic cell sensitivity to the preovulatory discharge of the hypothalamo-infundibular LRH tract, and perhaps also gonadotropins synthesis.

Animals↗