The hexB mismatch repair gene of Streptococcus pneumoniae: characterisation, cloning and identification of the product.

A second gene involved in mismatch repair in Streptococcus pneumoniae, the hexB gene, has been characterised. The gene was cloned into a multicopy plasmid vector. The cloned hexB gene is expressed as judged by its ability to complement a chromosomal hexB- allele. Its direction of transcription and its functional limits were defined. Comparison of the proteins encoded by recombinant plasmids and by restriction fragments allowed us to identify an Mr 83,000 protein as the probable product of the hexB gene. We offer evidence that this gene together with the hexA gene is essential for repair of transition as well as frameshift mismatches.