THE REC LOCUS, A COMPETENCE-INDUCED OPERON IN STREPTOCOCCUS-PNEUMONIAE

To study competence and the process of transformation (TFN) in pneumoc occi, we developed a method for isolating TFN- mutants using insertion al inactivation coupled with fusions to the gene for alkaline phosphat ase (phoA), One TFN- mutant transformed 2 log units less efficiently t han the parent strain, Reconstitution of the mutated region revealed a locus, rec, that contains two polycistronic genes, exp10 and the prev iously identified recA (B.Martin, J.M. Ruellan, J.F. Angulo, R. Devore t, and J.P. Claverys, Nucleic acids Res, 20:6412, 1992), Exp10 is like ly to be a membrane-associated protein, as it has a prokaryotic signal sequence and an Exp10-PhoA fusion localized with cell membranes. On t he basis of sequence similarity, pneumococcal RecA is a member of bact erial RecA proteins responsible for homologous recombination of DNA, D NA-RNA hybridization analysis showed that this locus is transcribed as a polycistronic message, with increased transcription occurring durin g competence, With an Exp10-PhoA chimera used as a reporter, there was a 10-fold increase in the expression of the rec locus during competen ce while there was only minimal expression under growth conditions tha t repressed competence, The TFN- mutant containing the exp10-phoA fusi on produced activator, a smalt extracellular polypeptide that induces competence, and the expression of rec was induced in response to activ ator, Therefore, the rec locus is directly required for genetic transf ormation and is regulated by the cell signaling mechanism that induces competence.