Sequence and stress-response analyses of the DNA mismatch repair gene hexAin Lactococcus lactis

The DNA mismatch repair gene hexA was identified in Lactococcus lactis by P CR amplification by using a pair of primers homologous to the DNA-binding D ps protein. The gene in its entirety, including the regulatory regions, was sequenced, by using a strategy of chromosomal walking based on two PCR pro tocols. The open reading frame of 2526 bp was preceded by a strong ribosome -binding site (AGGAAG) and was followed by a potential transcription termin ator (hairpin loop structure). The 5 ' terminus of the hexA mRNA was locate d 135 bp upstream of the start codon, and putative - 10 and - 35 regions we re identified. The deduced amino acid sequence revealed two motifs, the ATP /GTP-binding site (P-loop) and the "MutS family signature". The hexA promot er was cloned into pMU1327, which contained a promoter-less CAT reporter ge ne, and the promoter activity was examined under oxidative-stress condition s. It appears that the promoter activity is down-shifted by H2O2 at 4 mm.