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Publication Abstract from PubMed

Bacteriophage lambda encodes a DNA recombination system that includes a 5'-3' exonuclease (lambda Exo) and a single strand annealing protein (Redbeta). The two proteins form a complex that is thought to mediate loading of Redbeta directly onto the single-stranded 3'-overhang generated by lambda Exo. Here, we present a 2.3 A crystal structure of the lambda Exo trimer bound to three copies of the Redbeta C-terminal domain (CTD). Mutation of residues at the hydrophobic core of the interface disrupts complex formation in vitro and impairs recombination in vivo. The Redbeta CTD forms a three-helix bundle with unexpected structural homology to phage lambda Orf, a protein that binds to E. coli single-stranded DNA binding protein (SSB) to function as a recombination mediator. Based on this relationship, we found that Redbeta binds to full-length SSB, and to a peptide corresponding to its nine C-terminal residues, in an interaction that requires the CTD. These results suggest a dual role of the CTD, first in binding to lambda Exo to facilitate loading of Redbeta directly onto the initial single-stranded DNA (ssDNA) at a 3'-overhang, and second in binding to SSB to facilitate annealing of the overhang to SSB-coated ssDNA at the replication fork.

Crystal structure of the Redbeta C-terminal domain in complex with lambda Exonuclease reveals an unexpected homology with lambda Orf and an interaction with Escherichia coli single stranded DNA binding protein.,Caldwell BJ, Zakharova E, Filsinger GT, Wannier TM, Hempfling JP, Chun-Der L, Pei D, Church GM, Bell CE Nucleic Acids Res. 2019 Feb 28;47(4):1950-1963. doi: 10.1093/nar/gky1309. PMID:30624736^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.