DNA replication of bacteriophage T5. 3. Studies on the structure of concatemeric T5 DNA

The replication of bacteriophage T5 DNA has been shown to proceed via branched concatemeric intermediates. The structures of this concatemeric DNA was studied with respect to single-stranded regions and single-strand interruptions by digestion with S1 nuclease and agarose gel electrophoresis after alkali denaturation. The results were compared with the pattern of 'nicks' in the mature virion DNA, and the possible origins of these nicks are discussed. The structure of T5 concatemeric DNA was also studied by electron microscopy. Replication forks, loops and rare circular structures were observed, all of which were similar to those seen in replicating DNA of other large phages. Phage capsid structures were detected in association with both concatemeric and mature phage length DNA. These observations are discussed in relation to the replication, maturation and packaging of T5 DNA.