Bromouracil mutagenesis and mismatch repair in mutator strains of Escherichia coli.

A screening procedure based on the formation of papillae on individual bacterial colonies was used to isolate mutants of Escherichia coli with high mutation rates in the presence of bromouracil. Most of the mutants obtained had high spontaneous mutation rates and mapped close to the previously known mutators mutT, mutS, mutR, uvrE and mutL. Except for mutants of mutT type, these mutators also showed high mutability by bromouracil. Transfection experiments were performed with heteroduplex lambda DNA to test for mismatch repair. The results suggest a reduced efficiency of repair of mismatched bases in mutators mutS, mutR, uvrE and mutL, whereas mutants mapping as mutT appear normal. The results support a connection between spontaneous and bromouracil-induced mutability and repair of mismatched bases in DNA.