Structural basis for translocation by AddAB helicase-nuclease and its arrest at ? sites.

ABSTRACT: In bacterial cells, processing of double-stranded DNA breaks for repair by homologous recombination is dependent upon the recombination hotspot sequence ? (Chi) and is catalysed by either an AddAB- or RecBCD-type helicase-nuclease (reviewed in refs 3, 4). These enzyme complexes unwind and digest the DNA duplex from the broken end until they encounter a ? sequence, whereupon they produce a 3' single-stranded DNA tail onto which they initiate loading of the RecA protein. Consequently, regulation of the AddAB/RecBCD complex by ? is a key control point in DNA repair and other processes involving genetic recombination. Here we report crystal structures of Bacillus subtilis AddAB in complex with different ?-containing DNA substrates either with or without a non-hydrolysable ATP analogue. Comparison of these structures suggests a mechanism for DNA translocation and unwinding, suggests how the enzyme binds specifically to ? sequences, and explains how ? recognition leads to the arrest of AddAB (and RecBCD) translocation that is observed in single-molecule experiments.

SUBMITTER: Krajewski WW 

PROVIDER: S-EPMC3991583 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature