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 subtilis 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 greater than 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.