Intermediates in the maturation of bacteriophage lambda DNA

Intermediates in DNA maturation were studied in cells infected with temperature-sensitive mutants of phage λ. Bacteria were irradiated with UV to eliminate host DNA replication and then infected at high (nonpermissive) temperature with phage mutants in the head region of λ. Such genes have been implicated in the production of mature phage DNA. At various times after infection samples of culture were withdrawn for analysis both by viable phage assay and by sedimentation of extracted DNA in neutral and alkaline sucrose gradients. Portions of the infected cultures were also shifted down to low (permissive) temperatures and similar analyses carried out. The “rapidly sedimenting” immature DNA which accumulated under nonpermissive conditions in cells infected with mutants in genes A or E decreased under permissive conditions and at the same time material appeared in the region of mature molecules. This was not true in the case of mutants in genes B or C, where no mature molecules appeared after temperature shift-down. Assays for viable phage gave parallel results, and it was concluded that the rapidly sedimenting species observed during blocks in maturation are true intermediates.