SUMMARY: A gene was found in which encodes a protein highly homologous to the gene product, the S1 ribosomal protein. The protein contains the domain responsible for binding to ribosomes and two S1 motifs, instead of four as found in the protein. The protein is similar in this way to the equivalent protein of plant chloroplast ribosomes, supposed to be the counterpart of S1. The gene is expressed during vegetative growth in 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 situation, it can be inactivated without dramatic effects on cell viability. Southern hybridization of the DNA fragment encoding this gene revealed specific homologous fragments in all other Gram-positive bacteria tested. The hybridization pattern with suggests the presence of at least two homologous genes in this bacterium. We show that in the ORF preceding the homologue encodes a protein which is highly similar to the product of the gene which is located upstream of Again, in contrast to the situation, where these genes are co-transcribed, in they are separated by a transcription terminator and the homologue is transcribed during sporulation. We suggest that during the evolution very similar structures and genetic organization of these two genes were conserved but acquired different functions in Gram-negative and Gram-positive bacteria.


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