Restriction alleviation and enhancement of mutagenesis of the bacteriophage T4 chromosome in recBCsbcA strains of Escherichia coli.

The restriction of non glucosylated phage T4 DNA is reduced significantly in host bacterial strains carrying recBCsbcA mutations even in the presence of a functional rgl gene. In recBCsbcA hosts a high frequency of phage mutations are observed both in the glucosyl transferase genes and in the DNA sequences recognized by the rgl restriction enzymes. This hypermutagenic property of the recBCsbcA strains is not dependent on the glucosylation of the phage DNA, and the mutagenesis is localized to certain regions of the T4 chromosome. However, alleviation of rgl restriction in recBCsbcA strains is due neither to the increased mutagenesis, nor to the absence of a functional rgl system, since second site mutations (rra) restore rgl restriction, without affecting hypermutagenesis.