Mutants of bacteriophage T4 unable to cause breakdown of host DNA.

Abstract

Mutants in a number of genes of bacterlophage T4 were examined for their ability to cause breakdown of bacterial DNA after infection. To do this, a second mutation, one that completely blocks phage DNA synthesis, was "bred" into those mutants not already fully blocked in DNA synthesis, thus allowing direct observation of the fate of the bacterial DNA. It was found that mutants in genes 46 and 47 fail to cause breakdown of bacterial DNA. Introducing mutations in gene 46 or 47 into a mutant defective in dCTPase restores the ability of the dCTPase mutant to cause net synthesis of DNA after infection; this latter DNA probably contains some cytoslne in place of hydroxy-methyicytostne. These results Imply that genes 46 and 47 control one or more DNases and that these DNases preferentially attack DNA containing cytoslne rather than hydraxymethyicytoslne. It is not known, however, whether genes 46 and 47 are structural genes for a DNase or, instead, control an inducer or activator of a DNase.