The synthesis of coliphage T1 DNA: Degradation of the host chromosome

T1 derives most of the thymine for synthesis of its DNA from the host DNA. Nevertheless, degradation of host DNA to acid-soluble products cannot be observed even when synthesis of phage DNA is inhibited. The methods of inhibition were infection of a nonpermissive host with amber mutants with a DO (no DNA synthesis) phenotype, infection of a nonpermissive host with an amber mutant with a DA (DNA synthesis arrest) phenotype, shift to a nonpermissive temperature after infection with a ts mutant with a DO phenotype, and addition of nalidixic acid. We conclude that degradation of the host chromosome is linked to ongoing synthesis of phage DNA. During T1's development cycle, the bacterial nuclear region maintains a normal appearance by electron microscopy. Filling and filled phage heads are observed chiefly near the boundary of the nuclear region.