Binding Specificities of the Telomere Phage ?KO2 Prophage Repressor CB and Lytic Repressor Cro.

ABSTRACT: Temperate bacteriophages possess a genetic switch which regulates the lytic and lysogenic cycle. The genomes of the temperate telomere phages N15, PY54, and ?KO2 harbor a primary immunity region (immB) comprising genes for the prophage repressor (cI or cB), the lytic repressor (cro) and a putative antiterminator (q). The roles of these products are thought to be similar to those of the lambda proteins CI (CI prophage repressor), Cro (Cro repressor), and Q (antiterminator Q), respectively. Moreover, the gene order and the location of several operator sites in the prototype telomere phage N15 and in ?KO2 are reminiscent of lambda-like phages. We determined binding sites of the ?KO2 prophage repressor CB and lytic repressor Cro on the ?KO2 genome in detail by electrophoretic mobility shift assay (EMSA) studies. Unexpectedly, ?KO2 CB and Cro revealed different binding specificities. CB was bound to three OR operators in the intergenic region between cB and cro, two OL operators between cB and the replication gene repA and even to operators of N15. Cro bound exclusively to the 16 bp operator site OR3 upstream of the ?KO2 prophage repressor gene. The ?KO2 genes cB and cro are regulated by several strong promoters overlapping with the OR operators. The data suggest that Cro represses cB transcription but not its own synthesis, as already reported for PY54 Cro. Thus, not only PY54, but also phage ?KO2 possesses a genetic switch that diverges significantly from the switch of lambda-like phages.

SUBMITTER: Hammerl JA 

PROVIDER: S-EPMC4997575 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature