The Bacteriophage 434 Repressor Dimer Preferentially Undergoes Autoproteolysis by an Intramolecular Mechanism

Abstract

Inactivation of the lambdoid phage repressor protein is necessary to induce lytic growth of a lambdoid prophage. Activated RecA, the mediator of the host SOS response to DNA damage, causes inactivation of the repressor by stimulating the repressor's nascent autocleavage activity. The repressor of bacteriophage lambda and its homolog, LexA, preferentially undergo RecA-stimulated autocleavage as free monomers, which requires that each monomer mediates its own (intramolecular) cleavage. The cI repressor of bacteriophage 434 preferentially undergoes autocleavage as a dimer specifically bound to DNA, opening the possibility that one 434 repressor subunit may catalyze proteolysis of its partner subunit (intermolecular cleavage) in the DNAbound dimer. Here, we first identified and mutagenized the residues at the cleavage and active sites of 434 repressor. We utilized the mutant repressors to show that the DNA-bound 434 repressor dimer overwhelmingly prefers to use an intramolecular mechanism of autocleavage. Our data suggest that the 434 repressor cannot be forced to use an intermolecular cleavage mechanism. Based on these data, we propose a model in which the cleavage-competent conformation of the repressor is stabilized by operator binding.

Noncanonical DNA-binding mode of repressor and its disassembly by antirepressor

“…In contrast to the NDD, which contains several conserved positively charged residues, the MDD contains only one conserved positively charged residue (Arg129), suggesting that the MDD might serve as a dimerization domain without DNA-binding activity. The corresponding domain of the CI repressor is responsible for its autocleavage activity (15). The CAD forms an antiparallel coiled coil with two α12 helices (Fig.…”

“…To build the cis or trans models, NDD dimers were generated by superimposing Rep NDDs with the CI repressor (15). The modeled NDD-DNA complex was generated by superimposing Rep NDDs onto the DNA-bound structure of a Rep from phage 434 (17).…”

Identification and characterization of the immunity repressor (ImmR) that controls the mobile genetic element ICEBs1 of Bacillus subtilis

“…Activation of ICE Bs1 by the SOS response. The RecA‐dependent SOS response causes induction of many mobile elements (Walker, 1996; Gottesman and Weisberg, 2004; Dodd et al ., 2005; McCabe et al ., 2005; Quinones et al ., 2005). In many cases, this activation involves the RecA‐stimulated autocleavage of a repressor protein.…”

Environmental stress perception activates structural remodeling of extant Streptococcus mutans biofilms

“…However, after repeated IrvR pull-down screening experiments, we failed to identify any convincing protein interactions with IrvR other than its selfinteractions (i.e., homodimerization). While the bacteriophage λ CI repressor primarily autocleaves as a monomer 29,30 , both LexA and the 434 CI repressor autocleave while bound to DNA as a dimer 17,31 . Therefore, we were curious whether IrvR might directly trigger its own autocleavage via dimerization and/or DNA binding.…”