Isolation of a bacterial host selective for bacteriophage T4 containing cytosine in its DNA.

An Escherichia coli B strain, B834 galU56, has been isolated which supports growth of bacteriophage T4 with cytosine in its DNA while restricting growth of T4 with hydroxymethylcytosine. This host is partially deficient in uridine diphosphoglucose as determined by the ability of DNA isolated from T4 grown on it to accept glucose in an in vitro assay. In this mutant an intact rgl restriction system recognizes unglucosylated hydroxymethylcytosine residues in phage DNA, while the absence of a functional rB restriction function prevents degradation of unmodified DNA containing cytosine.