1887

Abstract

Deficiencies in the MutS protein disrupt methyl-directed mismatch repair (MMR), generating a mutator phenotype typified by high mutation rates and promiscuous recombination. How such deficiencies might arise in the natural environment was determined by analysing pathogenic strains of . Quantitative Western immunoblotting showed that the amount of MutS in a wild-type strain of the enterohaemorrhagic pathogen O157 : H7 decreased about 26-fold in stationary-phase cells as compared with the amount present during exponential-phase growth. The depletion of MutS in O157 : H7 is significantly greater than that observed for a laboratory-attenuated K-12 strain. In the case of stable mutators, defects in strains identified among natural isolates were analysed, including two O157 : H7 strains, a diarrhoeagenic O55 : H7 strain, and a uropathogenic strain from the reference (ECOR) collection. No MutS could be detected in the four strains by Western immunoblot analyses. RNase T2 protection assays showed that the strains were either deficient in transcripts or produced transcripts truncated at the 3′ end. Nucleotide sequence analysis revealed extensive deletions in the region of three strains, ranging from 7·5 to 17·3 kb relative to K-12 sequence, while the ECOR mutator contained a premature stop codon in addition to other nucleotide changes in the coding sequence. These results provide insights into the status of the gene and its product in pathogenic strains of .

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2003-05-01
2024-03-28
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