Functions of the mismatch repair gene mutS from Acinetobacter sp strain ADP1

The genus Acinetobacter encompasses a heterogeneous group of bacteria that are ubiquitous in the natural environment due in part to their ability to a dapt genetically to novel challenges. Acinetobacter sp. strain ADP1 (also k nown as strain BD413) is naturally transformable and takes up DNA from any source. Donor DNA can be integrated into the chromosome by recombination pr ovided it possesses sufficient levels of nucleotide sequence identity to th e recipient's DNA. In other bacteria, the requirement for sequence identity during recombination is partly due to the actions of the mismatch repair s ystem, a key component of which, MutS, recognizes mismatched bases in heter oduplex DNA and, along with MutL, blocks strand exchange. We have cloned mu tS from strain ADP1 and examined its roles in preventing recombination betw een divergent DNA and in the repair of spontaneous replication errors. Inac tivation of mutS resulted in 3- to 17-fold increases in transformation effi ciencies with donor sequences that were 8 to 20% divergent relative to the strain ADP1. Strains lacking MutS exhibited increased spontaneous mutation frequencies, and reversion assays demonstrated that MutS preferentially rec ognized transition mismatches while having little effect on the repair of t ransversion mismatches. Inactivation of mutS also abolished the marker-spec ific variations in transforming efficiency seen in mutS(+) recipients where transition and frameshift alleles transformed at eightfold lower frequenci es than transversions or large deletions. Comparison of the MutS homologs f rom five individual Acinetobacter strains with those of other gram-negative bacteria revealed that a number of unique indels are conserved among the A cinetobacter amino acid sequences.