The Properties of a Star Mutant of Phage T2

SUMMARY: The properties of a plaque-type variant, or 'star ' mutant, of coliphage T 2 are investigated. This mutant forms sectored plaques which are composed of approximately equal numbers of the parental star phage particles and of rapid-lysing ( r) mutants. The star mutant is shown to be a one-step mutant of wild-type, possess-ing a mutation at a locus, sl, that is close to the rl locus of phage T2. The r mutants occurring in the star plaques are all double-mutants, containing as well as the s1 mutation, a mutation at some further r locus. Rapid-lysing mutants isolated from different star plaques possess T mutations a t different loci. The high proportion of r mutants occurring in the star plaques is due to selection of r mutants that are formed spontaneously during replication of the star phage. This selection occurs during phage multiplication in Escherichia coli that is no longer multiplying ex-ponentially (old bacteria), but not in exponentially growing bacteria. The slow multiplication of star compared to r phage in old cultures of E. coli is not due to an inability of the old bacteria to synthesize star phage particles at the same rate as r phage particles, but is caused by two, probably related, factors. First, the sta