MucA protein affects spontaneous mutation in a localized region of Haemophilus influenzae.

A plasmid called pMucA, from a piece of the plasmid pKM101 (Mol. Gen. Genet 167 (1979) 317) cloned in the vector pDM2 (J. Bacteriol. 151 (1982) 1605), caused higher mutation in a local region of Haemophilus influenzae and caused even more mutation there in a strain also containing novC, the latter causing an increase in supercoiling (J. Bacteriol 164 (1985) 525). The novD mutation depressed supercoiling, and also depressed the mutation by pMucA in the local region of the chromosome. Thus, it is clear that supercoiling is an important phenomenon in spontaneous mutation of H. influenzae. The pMucA plasmid caused a number of other phenomena in H. influenzae, induced UV mutation (Proc. Natl. Acad. Sci. USA 82 (1985) 7753), decreased UV sensitivity of transforming DNA, but not cells, and UV-induced recombination of mutants of phage HP1c1. The effect of the MucA protein in mutagenesis of H. influenzae we consider to be due to the introduction of some of the E. coli functions from pKM101. We postulate that the localized mutation caused by the MucA plasmid also involved localization of the plasmid or its coded protein in the same area, resulting from binding to a homologous gene, probably rec-1, very close to the localized region.