[Effect of semipermissive conditions on recombination involving the early genes of bacteriophage T4 in amber-mutants. I. Effect of amber-mutation in gene 43].

Recombination frequencies between rII markers of bacteriophage T4 under conditions of partial inhibition of several early functions of the phage by amber mutations have been studied. Mutations in genes 33, 42 and 45 did not affect significantly recombination frequencies. Mutations in genes 32, 44 and 46 inhibited it. It has been found that effects of double mutations in pairs of genes: 43 and 30; 43 and 52; 43 and 33; 43 and 46; 43 and 32 were consistent with theoretically expected additive effects of corresponding single mutations. The presence of double mutations in pairs of genes: 43 and 41; 43 and 42, 43 and 44, 43 and 45 caused evident deviations from additivity. These deviations could reflect specific interactions of respective pairs of genes products under phage T4 recombination. Possible mechanisms of some of the effects observed are discussed.