Comparison of permuted region lengths in the genomes of related Salmonella typhimurium phages P22 and L.

Lengths of permuted regions in the P22 and L phage genomes were estimated from the relative yields of DNA in many electrophoretic bands obtained using several restriction endonucleases. It was found that 3.6 kb (8.7%) of P22-DNA and 7.2 kb (17.8%) of L-DNA were circularly permuted. In both phages the sequential packaging process proceeded in the same direction and four headful-size DNA molecules were, on the average, cleaved in one packaging series. The differences in circular permutation may originate from different genome lengths because their average headful portions are very similar (42.5 kb in P22 and 42.3 kb in L).