RNase H-defective mutants of Escherichia coli: a possible discriminatory role of RNase H in initiation of DNA replication |
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Authors: | Takashi Horiuchi Hisaji Maki and Mutsuo Sekiguchi |
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Institution: | (1) Department of Biology, Faculty of Science, Kyushu University 33, 812 Fukuoka, USA |
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Abstract: | 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.Abbreviations APr
ampicillin-resistant
- kb
kilobase pair(s)
- NEM
N-ethyl maleimide
- Ts
temperature-sensitive |
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