Should risk factors for breast cancer influence evaluation of breast abnormalities?
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Biopsy↗
Biomedical subjects
Cindy Levine
Publications and source records attributed to Cindy Levine.
I was dead wrong.
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Emergency Service, Hospital↗
Temporal regulation of topoisomerase IV activity in E. coli.
We isolated a mutant allele of dnaX, encoding the tau and gamma subunits of the DNA polymerase III holoenzyme, that causes extreme cell filamentation but does not affect either cell growth or DNA replication. This phenotype results from a defect in daughter chromosome decatenation during rapid growth. In these cells, ParC, one subunit of topoisomerase IV, no longer associated with the replication factory, as occurs in wild-type cells, and was instead distributed uniformly on the nucleoid; the distribution of ParE, the other subunit of topoisomerase IV, was unaffected. In addition, the majority of topoisomerase IV activity in synchronized cell populations was restricted to late in the cell cycle, when replication was essentially complete. These observations suggest that topoisomerase IV activity in vivo might be dependent on release of ParC from the replication factory.
Bacterial Proteins↗
SetB: an integral membrane protein that affects chromosome segregation in Escherichia coli.
SetB was identified as a high-copy suppressor of the partition defect of a mutation in parC, encoding one of the subunits of topoisomerase IV. Deletion of this integral inner membrane protein causes a delay in chromosome segregation, whereas its overproduction causes nucleoid disintegration and stretching, leading to a cell division defect. setB deletion mutants also exhibit a synthetic phenotype when combined with mutations that delete the C-terminal motor domain of the septal ring protein FtsK. SetB localizes in the cell as a helix and interacts with MreB, the bacterial actin homologue, which also forms a helix. These observations suggest that there may be a link between chromosome segregation and cellular infrastructure.
Cell Division↗
Topoisomerase III can serve as the cellular decatenase in Escherichia coli.
topB, encoding topoisomerase III, was identified as a high copy suppressor of the temperature-sensitive parC1215 allele, encoding one of the subunits of topoisomerase IV. Overexpression of topoisomerase III at the nonpermissive temperature was shown subsequently to restore timely chromosome decatenation and suppress lethality in strains carrying either temperature-sensitive parE or parC alleles. By developing an assay in vitro for precatenane unlinking, we demonstrated directly that both topoisomerase III and topoisomerase IV were efficient at this task, whereas DNA gyrase was very inefficient at precatenane removal. These observations suggest that precatenane unlinking is sufficient to sustain decatenation of replicating daughter chromosomes in the cell.
DNA Topoisomerases, Type I↗