Sublethal mutants of bacteriophage T4 affecting recombination and repair of DNA

A search was made for sublethal mutants to bacteriophage T4 defective in genetic recombination. T4D+ was mutagenized with proflavin, and phage from minute plaques was tested for their sensitivity to ultraviolet (uv) irradiation. Nine uv-sensitive mutants were found. Two exhibit decreased recombination, and the mutations are located in a previously unknown T4 gene--gene w. Seven other minute-plaque-making, uv sensitive mutants exhibit increased recombination; in each of these seven cases, the mutations were found to be in gene 58 (DNA-delay). The newly located gene w maps between genes 24 and 25. Mutants defective in gene w are sensitive to uv and to methyl methanesulfonate. They are also sensitive to hydroxyurea, although they degrade host DNA normally. Incorporation of 3H-thymidine into DNA is normal. A delayed and reduced phage yield appears to be caused by inefficient packaging of DNA in w mutants. This inefficient packaging appears to be caused by failure to form or to maintain a normal complement of concatemeric DNA. Genetic evidence indicates that both 58- and w mutants are defective in the same uv repair pathway as the uv sensitive T4 mutants x and y; none of the double mutants is more sensitive than each of the respective single mutants. Some of these double mutants, however, have cumulative effects on recombination, indicating a more complicated interaction than a discrete unilinear pathway. (U.S.)