Fragmentation of Bacillus bacteriophage phi105 DNA by complementary single-stranded DNA in the cohesive ends of the...

The structure of DNA from the temperate Bacillus subtilis phage phi105 was examined by using the restriction endonuclease EcoRI and by sedimentation analysis. The DNA contains six EcoRI cleavage sites. Although eight DNA fragments were identified in the EcoRI digests, the largest of these was shown to consist of the two fragments that carry the cohesive ends of the phage DNA. In neutral gradients, the majority of whole phi105 DNA sedimented as nicked circles and the remainder as oligomers. No unit-length linear structures were detected. The associated cohesive ends could be sealed by DNA ligase from Escherichia coli and could be cleaved by S1 nuclease. On the basis of these results and previously reported studies, it appears that, as isolated from phage particles, phi105 DNA is a circular molecule that is formed from the linear structure by the association of complementary single-stranded DNA.