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RNase H-defective mutants of Escherichia coli: A possible discriminatory role of RNase H in initiation of DNA replication

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Summary

Mutants of Escherichia coli completely deficient in RNase H activity were isolated by inserting transposon Tn3 into the structural gene for RNase H, rnh, and its promoter. These rnh - mutants exhibited the following phenotypes; (1) the mutants grew fairly normally, (2) rnh - cells could be transformed with ColE1 derivative plasmids, pBR322 and pML21, though the plasmids were relatively unstable, under non selective conditions, (3) rnh - mutations partially suppressed the temperature-sensitive phenotype of plasmid pSC301, a DNA replication initiation mutant derived from pSC101, (4) rnh - mutations suppressed the temperature-sensitive growth character of dnaA ts mutant, (5) rnh - cells showed continued DNA synthesis in the presence of chloramphenicol (stable DNA replication). Based on these findings we propose a model for a role of RNase H in the initiation of chromosomal DNA replication. We suggest that two types of RNA primers for initiation of DNA replication are synthesized in a dnaA/oriC-dependent and-independent manner and that only the dnaA/oriC-dependent primer is involved in the normal DNA replication since the dnaA/oriC independent primer is selectively degraded by RNase H.

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Abbreviations

APr :

ampicillin-resistant

kb:

kilobase pair(s)

NEM:

N-ethyl maleimide

Ts:

temperature-sensitive

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Communicated by M. Takanami

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Horiuchi, T., Maki, H. & Sekiguchi, M. RNase H-defective mutants of Escherichia coli: A possible discriminatory role of RNase H in initiation of DNA replication. Mol Gen Genet 195, 17–22 (1984). https://doi.org/10.1007/BF00332717

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  • DOI: https://doi.org/10.1007/BF00332717

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