IDENTIFICATION OF THE RPH (RNASE PH) GENE OF BACILLUS-SUBTILIS - EVIDENCE FOR SUPPRESSION OF COLD-SENSITIVE MUTATIONS IN ESCHERICHIA-COLI

A shotgun cloning of Bacillus sublilis DNA into pBR322 yielded a 2-kb fragment that suppresses the cold-sensitive defect of the nusA10(Cs) Escherichia coli mutant. The responsible gene encodes an open reading frame that is >50% identical at the amino acid level to the E. coli rph gene, which was formerly called orfE. This B. subtilis gene is located at 251-degrees adjacent to the gerM gene on the B. subtilis genetic map. It has been named rph because, like its E. coli analog, it encodes a phosphate-dependent exoribonuclease activity, RNase PH, that removes the 3' nucleotides from precursor tRNAs. The cloned B. subtilis rph gene also suppresses the cold-sensitive phenotype of other unrelated cold-sensitive mutants of E. coli, but not the temperature-sensitive phenotype of three temperature-sensitive mutants, including the nusA11(Ts) mutant, that were tested.