Biomedical subjects

A C Leonard

Publications and source records attributed to A C Leonard.

At least 19 recordsLinked to original sources

PubMed2001

Use of molecular markers to study the effects of environmental impacts on genetic diversity in brown bullhead (Ameirus nebulosus) populations.

Conservation biology needs sound biological information in order to maintain biological diversity in the face of the current rate of loss. An important component of the information needed is the level of genetic diversity within and between populations, especially for those species faced with exposure to environmental stressors. We applied multilocus DNA profile analysis (highly variable number tandem repeats [HVNTR] and randomly amplified polymorphic DNA [RAPD] techniques) and allozyme analysis to test whether individuals from historically degraded sites display levels of genetic diversity different from individuals taken from reference sites. Four Lake Erie tributaries, two impacted and two reference sites, were the sources of brown bullhead (Ameiurus nebulosus) samples. Pairwise comparison of the sampled populations demonstrated an association of decreased genetic diversity with exposure of brown bullhead to stressors using both RAPD and HVNTR analysis.

Animals↗

PubMed2000

IHF redistributes bound initiator protein, DnaA, on supercoiled oriC of Escherichia coli.

In Escherichia coli, initiation of chromosome replication requires that DnaA binds to R boxes (9-mer repeats) in oriC, the unique chromosomal replication origin. At the time of initiation, integration host factor (IHF) also binds to a specific site in oriC. IHF stimulates open complex formation by DnaA on supercoiled oriC in cell-free replication systems, but it is unclear whether this stimulation involves specific changes in the oriC nucleoprotein complex. Using dimethylsulphate (DMS) footprinting on supercoiled oriC plasmids, we observed that IHF redistributed prebound DnaA, stimulating binding to sites R2, R3 and R5(M), as well as to three previously unidentified non-R sites with consensus sequence (A/T)G(G/C) (A/T)N(G/C)G(A/T)(A/T)(T/C)A. Redistribution was dependent on IHF binding to its cognate site and also required a functional R4 box. By reducing the DnaA level required to separate DNA strands and trigger initiation of DNA replication at each origin, IHF eliminates competition between strong and weak sites for free DnaA and enhances the precision of initiation synchrony during the cell cycle.

Bacterial Proteins↗

PubMed1999

Drunken-cell footprints: nuclease treatment of ethanol-permeabilized bacteria reveals an initiation-like nucleoprotein complex in stationary phase replication origins.

The nucleoprotein complex formed on oriC, the Escherichia coli replication origin, is dynamic. During the cell cycle, high levels of the initiator DnaA and a bending protein, IHF, bind to oriC at the time of initiation of DNA replication, while binding of Fis, another bending protein, is reduced. In order to probe the structure of nucleoprotein complexes at oriC in more detail, we have developed an in situ footprinting method, termed drunken-cell footprinting, that allows enzymatic DNA modifying reagents access to intracellular nucleoprotein complexes in E.coli, after a brief exposure to ethanol. With this method, we observed in situ binding of Fis to oriC in exponentially growing cells, and binding of IHF to oriC in stationary cells, using DNase I and Bst NI endonuclease, respectively. Increased binding of DnaA to oriC in stationary phase was also noted. Because binding of DnaA and IHF results in unwinding of oriC in vitro, P1 endonuclease was used to probe for intracellular unwinding of oriC. P1 cleavage sites, localized within the 13mer unwinding region of oriC ', were dramatically enhanced in stationary phase on wild-type origins, but not on mutant versions of oriC unable to unwind. These observations suggest that most oriC copies become unwound during stationary phase, forming an initiation-like nucleoprotein complex.

Bacterial Proteins↗

PubMed1999

Hypothesis testing with the similarity index.

Multilocus DNA fingerprinting methods have been used extensively to address genetic issues in wildlife populations. Hypotheses concerning population subdivision and differing levels of diversity can be addressed through the use of the similarity index (S), a band-sharing coefficient, and many researchers construct hypothesis tests with S based on the work of Lynch. It is shown in the present study, through mathematical analysis and through simulations, that estimates of the variance of a mean S based on Lynch's work are downwardly biased. An unbiased alternative is presented and mathematically justified. It is shown further, however, that even when the bias in Lynch's estimator is corrected, the estimator is highly imprecise compared with estimates based on an alternative approach such as 'parametric bootstrapping' of allele frequencies. Also discussed are permutation tests and their construction given the interdependence of Ss which share individuals. A simulation illustrates how some published misuses of these tests can lead to incorrect conclusions in hypothesis testing.

DNA Fingerprinting↗

PubMed1997

Replication and segregation of a miniF plasmid during the division cycle of Escherichia coli.

Replication of the miniF plasmid pML31 was examined during the division cycle of Escherichia coli growing with doubling times between 40 and 90 min at 37 degrees C and compared to the replication of plasmid pBR322 and the minichromosome pAL70. The replication pattern of pML31 was indistinguishable from that of pBR322 at all growth rates and very different from the cell-cycle-specific replication of the minichromosome. It is concluded that both pML31 and pBR322 plasmids can replicate at all stages of the division cycle, with a probability of replication that increases gradually, but perhaps not exponentially, during the cycle. In contrast, the modes of segregation of pML31 and pBR322 plasmids into daughter cells at division appeared to differ, raising the possibility that pML31 may segregate in a nonrandom fashion similar to that of chromosomes and minichromosomes.

Cell Division↗

PubMed1996

Metabolites from an Antarctic sponge-associated bacterium, Pseudomonas aeruginosa.

In an ongoing survey of the bioactive potential of microorganisms associated with marine invertebrates, the culture media of a sponge-associated bacterial strain of Pseudomonas aeruginosa was found to contain metabolites which inhibit the growth of several Gram-positive microorganisms. A series of diketopiperazines (1-6) including a new natural product (6) and two known phenazine alkaloid antibiotics (7 and 8) were isolated from the culture broth of this bacterium.

Alkaloids↗

PubMed1995

Cell cycle-specific changes in nucleoprotein complexes at a chromosomal replication origin.

Initiation of DNA synthesis is triggered by the binding of proteins to replication origins. However, little is known about the order in which specific proteins associate with origin sites during the cell cycle. We show that in cycling cells there are at least two different nucleoprotein complexes at oriC. A factor for inversion stimulation (FIS)-bound nucleoprotein complex, present throughout the majority of the cell cycle, switches to an integration host factor (IHF)-bound form as cells initiate DNA replication. Coincident with binding of IHF, initiator DnaA binds to its previously unoccupied R3 site. In stationary phase, a third nucleoprotein complex forms. FIS is absent and inactive oriC forms a nucleoprotein structure containing IHF that is not observed in cycling cells. We propose that interplay between FIS and IHF aids assembly of initiation nucleoprotein complexes during the cell cycle and blocks initiation at inappropriate times. This exchange of components at replication origins is reminiscent of switching between pre- and post-replicative chromatin states at yeast ARS1.

Bacterial Proteins↗

PubMed1994

Children of disaster in the second decade: a 17-year follow-up of Buffalo Creek survivors.

OBJECTIVE: To conduct a long-term follow-up of child survivors of a devastating human-caused disaster. METHOD: Child survivors (2-15) of the Buffalo Creek dam collapse, first evaluated in 1974, 2 years postdisaster, were reevaluated 17 years postdisaster when they were adults. Of the original 207 children, 99 were located and reevaluated using ratings on the Psychiatric Evaluation Form, the Impact of Event Scale, and the SCL-90 and lifetime and current diagnoses from the Structured Clinical Interview for DSM-III-R. RESULTS: Ratings of psychiatric symptoms at the two points in time showed significant decreases in overall severity ratings and in anxiety, belligerence, somatic concerns, and agitation. A few symptoms, not present in the child sample, increased over time (substance abuse, suicidal ideation). The current rate of disaster-related post-traumatic stress disorder (PTSD) was 7%, down from a postflood rate of 32%. There were no differences by age group in current psychological status; however, women evidenced more PTSD-related symptoms than did men. All current PTSD cases were women. Comparisons with similar subjects from a nonexposed community showed no differences. CONCLUSIONS: The findings indicated that the children studied, although having shown earlier effects, had "recovered" from the event by the time of long-term follow-up.

Adaptation, Psychological↗

PubMed1994

The comorbidity of post-traumatic stress disorder and suicidality in Vietnam veterans.

Vietnam veterans (N = 232) recruited from three sources were assessed for suicidal thinking and behaviors, and symptoms of posttraumatic stress disorder (PTSD) and depression. Findings support the notion that suicidal thoughts are prevalent in this group, with veterans in psychotherapy reporting a greater likelihood of such symptoms (82.6%) than veterans in the community (35.7%) or those seeking assistance through a veteran's outreach center (66.7%). Thoughts of ending one's life and a previous suicide attempt were significantly correlated with a diagnosis of PTSD (r = .53, p < .001; and r = .33, p < .001, respectively). Veterans with a diagnosis of PTSD and depression or dysthymia were also more likely to report suicidal thinking and behaviors than veterans with only one of the diagnoses.

Adult↗

PubMed1993

Correlation of gene transcription with the time of initiation of chromosome replication in Escherichia coli.

Transcriptional levels of the Escherichia coli mioC and gidA genes, which flank the chromosomal origin of replication (oriC) and the dnaA gene, were correlated with the time of initiation of chromosome replication. The transcripts were measured either in dnaC2(ts) mutants that had been aligned for initiation of chromosome replication by a temperature shift or in synchronous cultures of cells obtained using the baby machine technique. In both types of experiments, mioC transcription was inhibited prior to initiation of chromosome replication and resumed several minutes after initiation. Conversely, gidA and dnaA transcription were both inhibited after initiation of replication, coincident with the period of hemimethylation of oriC DNA. It is proposed that mioC transcription prevents initiation of chromosome replication, and must terminate before replication can begin. It is further proposed that the eclipse period between rounds of replication, i.e. the minimum interval between successive initiations, encompasses the time required to methylate GATC sequences in newly replicated oriC plus the time required to terminate mioC transcription. Conversely, the active transcription of gidA and dnaA prior to initiation is consistent with their positive effects on initiation, and their shutdown after initiation could serve to limit premature reinitiation.

Algal Proteins↗

PubMed1992

Relationships between chromosome segregation, cell shape and temperature in Escherichia coli.

The partitioning of chromosomes into daughter cells during the division of Escherichia coli is non-random. As a result, the chromosome containing the older template DNA strand has a higher probability of segregating toward the old cell pole than toward the new cell pole. The numerical value of this probability is a function of the incubation temperature. It is shown here that a recent model for explaining the physiological basis for non-random chromosome segregation also explains the temperature dependence of the segregation process.

DNA Replication↗

PubMed1992

Chronic posttraumatic stress disorder and diagnostic comorbidity in a disaster sample.

Research has indicated significant comorbid psychopathology with chronic posttraumatic stress disorder (PTSD) in samples of war veterans. The present paper examines the issue of comorbidity in a disaster sample to learn whether findings from veterans generalized to this event. A total of 193 subjects exposed to the Buffalo Creek dam collapse of 1972 were examined 14 years later using diagnoses derived from the Structured Clinical Interview for DSM-III (SCID). Past and present PTSD was found in a significant portion of the sample. Major depression was the next most common diagnosis and was highly related to PTSD. Anxiety disorders were also common. The overlap with other diagnoses was quite similar to that found in a sample of Vietnam veterans we studied earlier, except that the disaster sample had fewer dysthymic disorders, substance abusers, and antisocial personality disorders. Possible explanations for comorbidity in chronic PTSD were discussed and it was suggested that the morphology of PTSD may be quite stable in at least some other nonveteran trauma populations.

Ambulatory Care↗

PubMed1992

Improved bacterial baby machine: application to Escherichia coli K-12.

Exponentially growing derivatives of Escherichia coli K-12 were immobilized onto the surfaces of nitrocellulose membrane filters which had been coated with poly-D-lysine. The cells attached firmly to the surfaces, and when flushed with culture medium, the immobilized cells continued to divide and newborn cells were released into the effluent. Cell cycle parameters were examined with the technique, and it was found that K-12 derivatives possessed differing values for interdivision times, C, D, and average cell sizes when grown in the same culture media. It was also found that the cells released from immobilized populations of one culture consisted of two predominant size classes: newborn cells of unit size with single nucleoids and newborn cells of double this unit size. The results demonstrated that K-12 derivatives can be used in the baby machine culture technique to examine all aspects of the cell cycle of this organism. Furthermore, the yield of newborn cells was about fivefold greater than that obtained previously with cultures of strain B/r immobilized onto uncoated membranes.

Bacteriological Techniques↗

PubMed1991

Children and disaster: age, gender, and parental effects on PTSD symptoms.

Psychiatric reports of 179 children aged 2 to 15 who were exposed to the Buffalo Creek dam collapse in 1972 were rated for post-traumatic stress disorder (PTSD) symptoms 2 years after the disaster. Age and gender effects and the impact of the level of exposure and parental functioning were examined according to a conceptual model addressing factors contributing to adaptation to a traumatic event. Results showed fewer PTSD symptoms in the youngest age group and higher symptom levels for girls than boys. Approximately 37% of the children were given a "probable" diagnosis of PTSD. Multiple regression analysis showed that life threat, gender, parental psychopathology, and an irritable and/or depressed family atmosphere all contributed to the prediction of PTSD symptomatology in the children.

Adaptation, Psychological↗

PubMed1990

Involvement of cell shape in the replication and segregation of chromosomes in Escherichia coli.

Chromosome replication appears to initiate in E. coli when the dnaA boxes in oriC become filled with DnaA protein, which could simultaneously mediate both the unwinding of the origin for the start of polymerization and the attachment of oriC to the cell envelope (Bramhill and Kornberg, 1988; Løbner-Olesen et al., 1989; Pierucci et al., 1989). The attachment takes place somewhere within the cell half in which the oriC resides. The boundaries of this attachment/replication zone, which cannot include the polar cap, could be demarcated by the polar and centrally located periseptal annuli (Rothfield, this Forum). Since attachment and polymerization are two aspects of the same process, the attachment probably takes place via the polymerizing strand. Once polymerization begins, the oriC with the older template strand moves away from the younger one, by mechanisms unknown, to eventually take up residence in the equivalent domain of the complementary sister cell. Thus, the template strand that stays within its domain corresponds to the strand that was attached during the previous round of replication, and the template that moves away is the one that was not attached. The driving force for this translocation is not specified by our model, but a number of plausible alternatives have been proposed by others (reviewed in Leonard and Helmstetter, 1990). Throughout the ensuing replication and cell division, the chromosomes are located (or can move freely) within the attachment/replication zone of the developing daughter cell (lateral cylinder and septum). At some time during the course of this process, but before the next initiation event, the replication origins must be released from the attachment sites so that the entire process can be repeated. Thus, the probabilistic non-random chromosome segregation is due to the asymmetry of the attachment/replication zone in the cell, whereas the partitioning system itself must possess a mechanism to discriminate between template strands of different ages. This apparent mechanistic relationship between chromosome replication, chromosome partitioning and the maintenance of cell shape may provide an interesting framework for future experiments.

Biomechanical Phenomena↗

PubMed1990

Buffalo Creek survivors in the second decade: stability of stress symptoms.

A follow-up study of 120 adult survivors of the Buffalo Creek dam collapse of 1972 showed group changes 14 years after the event. Decreased symptoms were noted in all areas, although significant psychopathology remained in about one-quarter of the survivors. A small group with delayed onset of symptoms was identified.

Adaptation, Psychological↗

PubMed1988

Replication patterns of multiple plasmids coexisting in Escherichia coli.

The replication patterns of several plasmids were measured simultaneously during the cell division cycle of Escherichia coli B/r. F plasmids harboring oriS, both oriS and oriV, pSC101, and pBR322 were found to replicate at all stages of the cell division cycle with kinetics which were indistinguishable from one another and clearly different from the periodic synthesis of the minichromosomes pAL49 and pAL70.

Cell Division↗

PubMed1987

Mechanism for chromosome and minichromosome segregation in Escherichia coli.

A mechanism for the segregation of chromosomes and minichromosomes into daughter cells during division of Escherichia coli is presented. It is based on the idea that the cell envelope contains a large number of sites capable of binding to the chromosomal replication origin, oriC, and that a polymerizing DNA strand becomes attached to one of the sites at initiation of a round of replication. The attachment sites are distributed throughout the actively growing cell envelope, i.e. lateral envelope and septum, but not in the existing cell poles. This asymmetric distribution of oriC attachment sites accounts for the experimentally observed non-random chromosome and minichromosome segregation, and for the variation in the degree of non-random segregation with cell strain and growth rate. The multi-site attachment concept also accounts for the unstable maintenance of minichromosomes.

Cell Division↗