The lysis mechanism of phage T4: Mutants affecting lysis

Abstract

A selection technique is used to isolate a new class of lysis-defective mutants of phage T4, the T4 amber t mutants. Under normal conditions, T4-infected bacteria lyse at a characteristic time after infection, each infected cell releasing a few hundred progeny phage. However, Su − bacteria infected with amber t mutant phage fail to lyse and continue to manufacture phage beyond the normal latent period even though phage lysozyme is present. Genetic crosses and complementation tests show that t mutant phage define a new T4 gene, gene t. Functional t gene product is required for the cessation of phage-infected cell metabolism at the characteristic lysis time. The T4 lysis mechanism is shown to be a sequential process of at least two steps: function of phage t gene product followed by function of phage e gene product. The e gene product, phage lysozyme, is known to degrade the host cell wall. It is proposed that the t gene product may be involved in degradation of the host cytoplasmic membrane.