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The RexA Protein of λ Phage: a New Member of a Classic Genetic Switch
Author(s) -
Schiltz Carl,
Thomason Lynn,
Hosford Chris,
Johnson Virginia,
Pan Hao,
Court Don,
Chappie Josh
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1055.17
Subject(s) - lysogen , lytic cycle , heteroduplex , lambda phage , lysogenic cycle , repressor , promoter , biology , binding site , bacteriophage , dna , genetics , biophysics , microbiology and biotechnology , gene , escherichia coli , gene expression , virus
The rexA and rexB genes of lambda phage act as a putative phage exclusion system to prevent superinfection of lambda lysogens by other lytic phages. The Rex exclusion system was thought to act as an internal suicide mechanism by which soluble RexA would bind RexB localized on the inner membrane, causing RexB to open as an ion channel, depolarizing the membrane and leading to cell death. Genetic data suggests that RexA can function independently of RexB to induce the lytic promoters of the lambda lysogen. Additionally, RexA must exist at a higher concentration than RexB in vivo to produce the lytic response. Through genetic data and in vitro binding assays, we have also shown that RexA interacts with cI repressor protein, the factor needed to repress lytic promoters in the lambda lysogen. Intriguingly, RexA is capable of stably binding lambda operator DNA in vitro . We have also solved the structure of RexA to 2.05Å resolution. The structure identifies RexA as existing as a constitutive dimer, each monomer consisting of a split dimerization and globular domain. An electrostatic potential map of the structure shows a region of high positive charge at the interface of the two globular domains, indicating a potential region for DNA binding; however, there is not sufficient space between the dimers to facilitate binding in this crystal form. In addition, RexA shares some structural similarity with bacterial recombination‐associated RdgC protein. Structural superposition with RdgC and normal mode analysis in addition to the electron density map hints at a possible conformational change in RexA upon cI and/or DNA binding. RexA thus appears to function as a master regulator of the classic lambda phage genetic switch. With this in mind, we are now attempting to parse out the specific interactions between RexA and cI and/or DNA that allow for induction of the lytic promoters.