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

✍ Scribed by Horiuchi, Takashi ;Maki, Hisaji ;Sekiguchi, Mutsuo

• Publisher: Springer
• Year: 1984
• Tongue: English
• Weight: 632 KB
• Volume: 195
• Category: Article
• ISSN: 0026-8925
• DOI: 10.1007/bf00332717

✦ Synopsis

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 dnaAts 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.