Isolation of mutations defining five new cistrons essential for development of bacteriophage Mu

Abstract

Three hundred new mutant strains of bacteriophage Mu with amber mutations in essential genes were isolated and characterized. Measurement of complementation between these new strains and strains carrying mutations in previously identified complementation groups revealed the existence of five new complementation groups: T, U, V, W, and Y. In general, mixed infection of cells by phage carrying mutations in different cistrons resulted in the production of a normal burst of 50 to 200 phage per cell; however, mixed infection with phage carrying mutations in certain pairs of adjacent cistrons gave a 10- to 20-fold lower burst of only 3 to 30 phage per cell. Cistron pairs which showed this reduced complementation were D- E, H- F, J- K, Y- N, Q- V, W- R, and S- U. In addition, mutations assigned to cistron I fell into three groups on the basis of their complementation behavior; phage carrying mutations in one group located at one end of the cistron showed weak complementation with phage carrying mutations in a second group at the opposite end of the cistron, but phage carrying mutations in the third group located between the first two groups showed no complementation with members of any of the three groups. The complementation analysis also showed that mutations previously assigned to separate complementation groups O and P really belong to a single complementation group P.