The mutK gene of Vibrio cholerae: a new gene involved in DNA mismatch repair

A new gene, mutK, of Vibrio cholerae, encoding a 19-kDa protein which is in volved in repairing mismatches in DNA via a presumably methyl-independent p athway, has been identified. The product of the mutK gene cloned in either high- or low-copy-number vectors can reduce the spontaneous mutation freque ncy of Escherichia call mutS, mutL, mutU, and dam mutants. The spontaneous mutation frequency of a chromosomal mutK knockout mutant was almost identic al to that of wild-type V. cholerae cells, indicating that when the methyl- directed mismatch repair is blocked, the repair potential of MutK becomes a pparent. The complete nucleotide sequence of the mutK gene has been determi ned, and the deduced amino acid sequence showed three open reading frames ( ORFs), of which the ORF3 represents the mutK gene product, The mutK gene pr oduct has no significant homology with any of the proteins deposited in the EMBL data bank ORF2, located upstream of mutK, encodes a 14-kDa protein wh ich has more than 70% homology,vith a hypothetical protein found only downs tream of the E. coli vsr gene. ORF1, located farther upstream of mutK, has more than 80% homology with a major cold shock protein found in several bac teria. Downstream of mutK, a partial ORF having 60% homology with an RNA me thyltransferase has been identified. The mutK gene has recently been positi oned in the ordered cloned DNA map of the genome of the V. cholerae strain from which the gene was isolated (10).