Autoregulation of repressor synthesis in bacteriophage λimm434

A 550-bp DNA fragment derived from the immunity region of phage lambda imm434 and carrying the wild-type prm promoter has been inserted upstream of the lacZ gene, in the beta 2 region of an 'in-vitro'-constructed transducing phage. In strains lysogenized with this phage, the rates of transcription from the 434-prm promoter can be assayed as units of beta-galactosidase in the absence or in the presence of increasing levels of 434 repressor. The results obtained indicate the existence of a mechanism of autoregulation for repressor maintenance in strains lysogenic for wild-type phage 434. The rate of transcription from prm in a (434) lysogen is of the same magnitude as that in a (lambda ) lysogen, and, as in the case of lambda , high levels of repressor repress prm whereas low levels stimulate it. An estimation of the strength of the leftward promoters located in the right half of the lambda beta 2 region compared with 434 prm was also obtained.