Mutagenic topography of the E. coli chromosome.

The lactose fermenting genes in E. coli have been transposed to various chromosomal locations. The bacterial strains were mutagenized with different chemical mutagens and the frequency of Lac negative mutant colonies was measured as a function of lactose gene location in the chromosome. There appears to be a highly mutable location between 58-60 minutes on the E. coli map. This region does not appear to be correlated with the origin of DNA replication or with the terminus. The possible significance of this mutable region in the evolution of new bacterial genes is discussed.