The isolation and characterization of a T4 mutant partially defective in recombination

Summary Starting with an rII diploid isolate of T4 a procedure is reported for isolating diploid variants which generate segregants at a reduced frequency. The properties of one such variant, which exhibits a four-fold reduction in segregation frequency, is discussed in detail. It is shown: 1) this variant has acquired at least two extra mutations outside the rII region 2) these mutations confer a four to seven-fold reduction in recombination frequency as measured in standard phage crosses 3) the mutations also cause a 20% increase in UV-sensitivity and a marked effect both on multiplicity-reactivation and on the intracellular development of radiation-resistance.