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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The only DNA helicase essential for Escherichia coli viability is DnaB, the chromosome replication fork helicase. In contrast, in Bacillus subtilis, in addition to the DnaB counterpart called DnaC, we have found a second essential DNA helicase, called PcrA. It is 40% identical to the Rep and UvrD DNA helicases of E. coli and 61% identical to the PcrA helicase of Staphylococcus aureus. This gene is located at 55° on the chromosome and belongs to a putative operon together with a ligase gene (lig ) and two unknown genes named pcrB and yerH. As PcrA was essential for cell viability, conditional mutants were constructed. In such mutants, chromosomal DNA synthesis was slightly decreased upon PcrA depletion, and rolling-circle replication of the plasmid pT181 was inhibited. Analysis of the replication intermediates showed that leading-strand synthesis of pT181 was prevented upon PcrA depletion. To compare PcrA with Rep and UvrD directly, the protein was produced in rep and uvrD mutants of E. coli. PcrA suppressed the UV sensitivity defect of a uvrD mutant but not its mutator phenotype. Furthermore, it conferred a Rep− phenotype on E. coli. Altogether, these results show that PcrA is an helicase used for plasmid rolling-circle replication and suggest that it is also involved in UV repair.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Escherichia coli loses its rod shape by inactivation of PBP2 (penicillin-binding protein 2), target of the β-lactam mecillinam. Under these conditions, cell division is blocked in rich medium. Division in the absence of PBP2 activity is restored (and resistance to mecillinam is conferred) when the three cell division proteins FtsQ, FtsA and FtsZ are overproduced, but not when only one or two of them are overproduced. Division in the absence of PBP2 activity is also restored by a doubling in the ppGpp pool, as in the argS201 mutant. However, the nucleotide ppGpp, a transcriptional regulator of many operons, does not govern any of the five promoters of the ftsQAZ operon, as shown by S1 mapping of ftsQAZ mRNA 5′ ends in exponentially growing wild-type cells in the mecillinam-resistant argS201 mutant (intermediate ppGpp level) or during the stringent response elicited by isoleucine starvation (high ppGpp level). Furthermore, the concentration of FtsZ protein is not increased in exponentially growing mecillinam-resistant argS201 cells. These results show that the ftsQAZ operon is not the ppGpp target responsible for mecillinam resistance. We are currently trying to identify those targets that, at intermediate ppGpp levels, allow cells to divide as spheres in the absence of PBP2.
    Type of Medium: Electronic Resource
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