Elements in the ? Immunity Region Regulate Phage Development: Beyond the "Genetic Switch"

Author:

Thomason,Lynn

Morrill, Kathleen

Murray, Gillian

Court,Carolyn

Shafer, Brenda

Schneider,Tom

Court,Don
Author Address

Basic Science Program, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702., University of Massachusetts Medical School, Albert Sherman Building, 4th Floor, Room 1066, 368 Plantation St, Worcester, MA, 01605., University of Maryland School of Medicine, 655 West Baltimore Street, Baltimore, Maryland, 21201., RNA Biology Laboratory, National Cancer Institute, Frederick, MD, 21702.,

Abstract:

Genetic elements in the bacteriophage ? immunity region contribute to stable maintenance and synchronous induction of the integrated E. 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 (PL and PR ) and lysogenic (PRM ) promoters, referred to as the Genetic Switch. Other less well-characterized elements in the phage immunity region include the PLIT promoter and the immunity terminator, TIMM . The PLIT promoter is repressed by the bacterial LexA protein in ? lysogens. LexA repressor, like the ? CI repressor, is inactivated during the SOS response to DNA damage, and this regulation ensures that the PLIT promoter and the lytic PL and PR promoters are synchronously activated. Proper RexA and RexB protein levels are critical for the switch from lysogeny to lytic growth. Mutation of PLIT 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, TIMM , is a Rho-independent, intrinsic terminator. Inactivation of TIMM has minimal effect on ? lysogenization or prophage induction. © 2019 John Wiley & Sons Ltd.

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