Two suppressor loci for gene 49 mutations of bacteriophage T4. II. DNA and capsid maturation.

Introduction into T4am49-defective phage of secondary mutations at either of two loci on the T4 chromosome results in suppression of the inability of these phage to grow on E. coli B. These mutations alter certain aspects of the 49-defective phenotype while not affecting others. The unusually rapid sedimentation rate of 49-defective replicative DNA is almost completely suppressed by mutations at either site. Likewise, the abnormal accumulation of incompletely filled phage capsids due to the 49-mutation is also suppressed, although the suppressor mutations themselves lead to a similar but less drastic phenotype. In contrast, the loss of a hydrolytic activity in 49-defective infections is not restored by the suppressor mutations. This lends some weight to the suggestion that the absence of that activity is not the result of the 49-phenotype but rather the cause of it. These secondary mutations also result in the production of a heterogeneous population of DNA molecules similar to but generally shorter than mature phage DNA. The molecules fail to become stably associated with phage capsids. This and the DNA arrest phenotype of these phages described previously account for the low yield of the pseudorevertant and suppressor phages.