Summary
Escherichia coli rnh mutants deficient in ribonuclease H (RNase H) are capable of DNA replication in the absence of protein synthesis. This constitutive stable DNA replication (SDR) is dependent upon the recA + gene product. The requirement of SDR for recA + can be suppressed by rin mutations (for recA+-independent), or by lexA(Def) mutations which inactivate the LexA repressor. Thus, there are at least three genetically distinct types of SDR in rnh mutants: recA +-dependent SDR seen in rnh - rin+ lexA+ strains, recA +-independent in rnh - rin- lexA+, and recA +-independent in rnh - rin+ lexA(Def). The expression of SDR in rin - and lexA(Def) mutants demonstrated a requirement for RNA synthesis and for the absence of RNase H. The suppression of the recA + requirement by rin mutations was shown to depend on some new function of the recF + gene product. In contrast, the suppression by lexA-(Def) mutations was not dependent on recF +. The lexA3 mutation inhibited recA +-dependent SDR via reducing the amount of recA + activity available, and was suppressed by the recAo254 mutation. The SDR in rnh - rin- cells was also inhibited by the lexA3 mutation, but the inhibition was not reversed by the recAo254 mutation, indicating a requirement for some other lexA +-regulated gene product in the recA +-independent SDR process. A model is presented for the regulation of the expression of these three types of SDR by the products of the lexA +, rin+ and recF + genes.
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Communicated by R. Devoret
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Torrey, T.A., Kogoma, T. Genetic analysis of constitutive stable DNA replication in rnh mutants of Escherichia coli K12. Mol Gen Genet 208, 420–427 (1987). https://doi.org/10.1007/BF00328133
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DOI: https://doi.org/10.1007/BF00328133