IDENTIFICATION OF THE STREPTOCOCCAL COMPETENCE-PHEROMONE RECEPTOR

Competence for genetic transformation in certain species of streptococ ci has been known for many years to be induced by a secreted protease- sensitive pheromone, referred to as the competence factor or activator , which acts as a quorum-sensing signal to co-ordinate expression of l ate competence genes. We recently reported identification of the phero mone of Streptococcus pneumoniae strain Rx as a small unmodified pepti de, which was termed competence-stimulating peptide (CSP). By identify ing the gene (comC) encoding the Rx CSP we were able to show that it i s synthesized as a precursor peptide containing an N-terminal double-g lycine type leader, In the present work, we describe two alleles of th e corresponding gene from Streptococcus gordonii strains Challis and N CTC 7865, which are strains with distinct competence pheromones and co rresponding specific pheromone reactivities. In addition, the nucleic acid sequences of two genes located downstream of comC were determined ; interestingly, these genes encode a two-component signal transductio n system, We therefore speculated that their products, a histidine kin ase (ComD) and its cognate response regulator (ComE), act downstream o f the CSP in competence regulation, By tracing the CSP specificity of the competence response in these strains to strain-specific alleles of comD, we obtained evidence demonstrating that the histidine kinase Co mD is the competence-pheromone receptor.