THE BACILLUS-SUBTILIS CHROMOSOME REGION ENCODING HOMOLOGS OF THE ESCHERICHIA-COLI MSSA AND RPSA GENE-PRODUCTS

A gene was found in Bacillus subtilis which encodes a protein highly h omologous to the Escherichia coli rpsA gene product, the S1 ribosomal protein. The B. subtilis protein contains the domain responsible for b inding to ribosomes and two S1 motifs, instead of four as found in the E. coli protein. The B. subtilis protein is similar in this way to th e equivalent protein of plant chloroplast ribosomes, supposed to be th e counterpart of E. coli S1. The gene is expressed during vegetative g rowth in B. subtilis at the transcriptional and translational levels, as judged by Northern hybridization and expression in a translational fusion with a reporter gene, In contrast to the E. coli situation, it can be inactivated without dramatic effects on cell viability, Souther n hybridization of the B. subtilis DNA fragment encoding this gene rev ealed specific homologous fragments in all other Gram-positive bacteri a tested, The hybridization pattern with B. stearothermophilus suggest s the presence of at least two homologous genes in this bacterium, We show that in B. subtilis the ORF preceding the rpsA homologue encodes a protein which is highly similar to the product of the E. coli mssA g ene which is located upstream of rpsA, Again, in contrast to the E. co li situation, where these genes are co-transcribed, in B. subtilis the y are separated by a transcription terminator and the mssA homologue i s transcribed during sporulation. We suggest that during the evolution very similar structures and genetic organization of these two genes w ere conserved but acquired different functions in Cram-negative and Gr am-positive bacteria.