Elements in the λ immunity region regulate phage development: beyond the 'Genetic Switch'.

ABSTRACT: Genetic elements in the bacteriophage λ immunity region contribute to stable maintenance and synchronous induction of the integrated Escherichia coli prophage. There is a bistable switch between lysogenic and lytic growth that is orchestrated by the CI and Cro repressors acting on the lytic (P_L and P_R ) and lysogenic (P_RM ) promoters, referred to as the Genetic Switch. Other less well-characterized elements in the phage immunity region include the P_LIT promoter and the immunity terminator, T_IMM . The P_LIT promoter is repressed by the bacterial LexA protein in λ lysogens. LexA repressor, like the λ CI repressor, is inactivated during the SOS response to DNA damage, and this regulation ensures that the P_LIT promoter and the lytic P_L and P_R promoters are synchronously activated. Proper RexA and RexB protein levels are critical for the switch from lysogeny to lytic growth. Mutation of P_LIT reduces RexB levels relative to RexA, compromising cellular energetics and causing a 10-fold reduction in lytic phage yield. The RexA and RexB proteins interact with themselves and each other in a bacterial two-hybrid system. We also find that the transcription terminator, T_IMM , is a Rho-independent, intrinsic terminator. Inactivation of T_IMM has minimal effect on λ lysogenization or prophage induction.

SUBMITTER: Thomason LC 

PROVIDER: S-EPMC8103288 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature