Unbiased participation of T 4 phage DNA strands in replication

Abstract

Nitrocellulose filters were charged with right or with left strands of T 4 DNA preparatively isolated by the procedure of Guha and Szybalski (1968). Replicative hybrid (of labeled parental DNA) and progeny phage DNA's were annealed, using differentially labeled DNA from mature phage as an internal control. In T 4 phage infection of E.coli B (with either wild or ligase negative Amber mutant), both parental strands of DNA participate in semiconservative replication. An equal proportion of DNA from each parental strand is transferred also to progeny phage. Newly synthesized progeny DNA is also composed of left and right strands. This is true even at the earliest times of DNA synthesis (4-4:30), that is when less than 10% of the length of the parental molecule has been replicated. These observations apply both to wild and to ligase-negative T 4 phages. Both strands are also produced in E.coli B infected with the ligase negative mutant in the presence of CM added for a period, early after infection which permits, after removal, a considerable yield of phage.