Sequence analysis of a region from the early right operon in phage P22 including the replication genes 18 and 12

A comparison of a 3000-bp sequence of Salmonella phage P22, coding for gene c1 and the replication genes 18 and 12, with the analogous cII-O-P region of coliphage lambda permits the localization of transcriptional signals, an oop RNA species, and the origin of replication (ori) within gene 18. Gene c1 and the amino terminal region of gene 18 show homology to the respective lambda genes. In the ori domain of the replicator proteins the homology to phi 82 is most pronounced. Of two lambda:repP22 hybrids (lambda with replication genes of P22) analysed, one codes for a hybrid O/18 protein with 30 N-terminal amino acids coded for by lambda. Gene 12 is nonhomologous to its lambda counterpart (gene P), but closely related to dnaB of Escherichia coli. A ren gene is missing, whereas two open reading frames (ORFs) distal to gene 12 are almost identical to those in the lambda nin region. We try to account for the occurrence and location of highly conserved sequences among the lambdoid phages by assigning them a role in recombinational reassortment of functional units during the evolution of this phage family.