Dataset Information

Insensitivity of chromosome I and the cell cycle to blockage of replication and segregation of Vibrio cholerae chromosome II.

ABSTRACT:

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Vibrio cholerae has two chromosomes (chrI and chrII) whose replication and segregation are under different genetic controls. The region covering the replication origin of chrI resembles that of the Escherichia coli chromosome, and both origins are under control of the highly conserved initiator, DnaA. The origin region of chrII resembles that of plasmids that have iterated initiator-binding sites (iterons) and is under control of the chrII-specific initiator, RctB. Both chrI and chrII encode chromosome-specific orthologs of plasmid partitioning proteins, ParA and ParB. Here, we have interfered with chrII replication, segregation, or both, using extra copies of sites that titrate RctB or ParB. Under these conditions, replication and segregation of chrI remain unaffected for at least 1 cell cycle. In this respect, chrI behaves similarly to the E. coli chromosome when plasmid maintenance is disturbed in the same cell. Apparently, no checkpoint exists to block cell division before the crippled chromosome is lost by a failure to replicate or to segregate. Whether blocking chrI replication can affect chrII replication remains to be tested.

Importance

Chromosome replication, chromosome segregation, and cell division are the three main events of the cell cycle. They occur in an orderly fashion once per cell cycle. How the sequence of events is controlled is only beginning to be answered in bacteria. The finding of bacteria that possess more than one chromosome raises the important question: how are different chromosomes coordinated in their replication and segregation? It appears that in the evolution of the two-chromosome genome of V. cholerae, either the secondary chromosome adapted to the main chromosome to ensure its maintenance or it is maintained independently, as are bacterial plasmids. An understanding of chromosome coordination is expected to bear on the evolutionary process of chromosome acquisition and on the efficacy of possible strategies for selective elimination of a pathogen by targeting a specific chromosome.

SUBMITTER: Kadoya R

PROVIDER: S-EPMC3350373 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Insensitivity of chromosome I and the cell cycle to blockage of replication and segregation of Vibrio cholerae chromosome II.

Kadoya Ryosuke R Chattoraj Dhruba K DK

mBio 20120508 3

<h4>Unlabelled</h4>Vibrio cholerae has two chromosomes (chrI and chrII) whose replication and segregation are under different genetic controls. The region covering the replication origin of chrI resembles that of the Escherichia coli chromosome, and both origins are under control of the highly conserved initiator, DnaA. The origin region of chrII resembles that of plasmids that have iterated initiator-binding sites (iterons) and is under control of the chrII-specific initiator, RctB. Both chrI a ...[more]

PMID: 22570276

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Project description:ABSTRACT Bacterial ParA and ParB proteins are best known for their contribution to plasmid and chromosome segregation, but they may also contribute to other cell functions. In segregation, ParA interacts with ParB, which binds to parS centromere-analogous sites. In transcription, plasmid Par proteins can serve as repressors by specifically binding to their own promoters and, additionally, in the case of ParB, by spreading from a parS site to nearby promoters. Here, we have asked whether chromosomal Par proteins can likewise control transcription. Analysis of genome-wide ParB1 binding in Vibrio cholerae revealed preferential binding to the three known parS1 sites and limited spreading of ParB1 beyond the parS1 sites. Comparison of wild-type transcriptomes with those of ?parA1, ?parB1, and ?parAB1 mutants revealed that two out of 20 genes (VC0067 and VC0069) covered by ParB1 spreading are repressed by both ParB1 and ParA1. A third gene (VC0076) at the outskirts of the spreading area and a few genes further away were also repressed, particularly the gene for an outer membrane protein, ompU (VC0633). Since ParA1 or ParB1 binding was not evident near VC0076 and ompU genes, the repression may require participation of additional factors. Indeed, both ParA1 and ParB1 proteins were found to interact with several V. cholerae proteins in bacterial and yeast two-hybrid screens. These studies demonstrate that chromosomal Par proteins can repress genes unlinked to parS and can do so without direct binding to the cognate promoter DNA. IMPORTANCE Directed segregation of chromosomes is essential for their maintenance in dividing cells. Many bacteria have genes (par) that were thought to be dedicated to segregation based on analogy to their roles in plasmid maintenance. It is becoming clear that chromosomal par genes are pleiotropic and that they contribute to diverse processes such as DNA replication, cell division, cell growth, and motility. One way to explain the pleiotropy is to suggest that Par proteins serve as or control other transcription factors. We tested this model by determining how Par proteins affect genome-wide transcription activity. We found that genes implicated in drug resistance, stress response, and pathogenesis were repressed by Par. Unexpectedly, the repression did not involve direct Par binding to cognate promoter DNA, indicating that the repression may involve Par interactions with other regulators. This pleiotropy highlights the degree of integration of chromosomal Par proteins into cellular control circuitries.

Dataset Information

Insensitivity of chromosome I and the cell cycle to blockage of replication and segregation of Vibrio cholerae chromosome II.

Unlabelled

Importance

Publications

Insensitivity of chromosome I and the cell cycle to blockage of replication and segregation of Vibrio cholerae chromosome II.

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