CONTROL OF RECOMBINATION RATE DURING TRANSFORMATION OF STREPTOCOCCUS-PNEUMONIAE - AN OVERVIEW

Despite the fact that natural transformation was described long ago in Streptococcus pneumoniae, only a limited number of recombination gene s have been identified, Two of them have recently been characterized a t the molecular level, recA which encodes a protein essential for homo logous recombination and mmsA which encodes the homologue of the Esche richia coli RecG protein, After a survey of the available information regarding the function of RecA, RecG, and other proteins such as the m ismatch repair proteins HexA and HexB that can affect the outcome of r ecombinants, the different levels at which horizontal genetic exchange can be controlled are discussed, It is shown that the specific induct ion of the recA gene which occurs in competent cells is required for f ull recombination proficiency, Results regarding the ability of the He x generalized mismatch repair system to prevent recombination between partially divergent sequences during transformation are also summarize d, A structural analysis of homeologous recombinants which suggests th at formation of mosaic recombinants can occur independently of mismatc h repair in a single-step transformation is also reported, Finally, ar guments in favor of an evolutionary origin of transformation as a mean s of genome evolution are discussed and the different types of recombi nation events observed which could potentially contribute to S. pneumo niae genome evolution are listed.