Identification of a putative Bacillus subtilis rho gene

Transposon Tn917 mutagenesis of Bacillus subtilis BD99 followed by selection for protonophore resistance led to the isolation of strain MS119, which contained a single Tn917 insertion in an open reading frame whose deduced amino acid sequence was 56.6% identical to that of the Escherichia coli rho gene product. The insertional site was near the beginning of the open reading frame, which was located in a region of the B. subtilis chromosome near the spo0F gene; new sequence data for several open reading frames surrounding the putative rho gene are presented. The predicted B. subtilis Rho protein would have 427 amino acids and a molecular weight of 48,628. The growth of the mutant strain was less than that of the wild type on defined medium at 30°C. On yeast extract-supplemented medium, the growth of MS119 was comparable to that of the wild type on defined medium at 30°C. On yeast extract-supplemented medium, the growth of MS119 was comparable to that of the wild type at 30°C but was much slower at lower temperatures; sporulation occurred and competence was developed in cells of the mutant grown at 30°C. To determine whether the protonophore resistance and sensitivity to low growth temperature resulted from the insertion, a chloramphenicol resistance cassette was inserted into the wild-type B. subtilis rho gene of strain BD170; the resulting derivative displayed the same phenotype as MS119.