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Publication Abstract from PubMed

Mycobacterial AdnAB is a heterodimeric helicase-nuclease that initiates homologous recombination by resecting DNA double-strand breaks (DSBs). The AdnA and AdnB subunits are each composed of an N-terminal motor domain and a C-terminal nuclease domain. Here we report cryoelectron microscopy (cryo-EM) structures of AdnAB in three functional states: in the absence of DNA and in complex with forked duplex DNAs before and after cleavage of the 5' single-strand DNA (ssDNA) tail by the AdnA nuclease. The structures reveal the path of the 5' ssDNA through the AdnA nuclease domain and the mechanism of 5' strand cleavage; the path of the 3' tracking strand through the AdnB motor and the DNA contacts that couple ATP hydrolysis to mechanical work; the position of the AdnA iron-sulfur cluster subdomain at the Y junction and its likely role in maintaining the split trajectories of the unwound 5' and 3' strands. Single-molecule DNA curtain analysis of DSB resection reveals that AdnAB is highly processive but prone to spontaneous pausing at random sites on duplex DNA. A striking property of AdnAB is that the velocity of DSB resection slows after the enzyme experiences a spontaneous pause. Our results highlight shared as well as distinctive properties of AdnAB vis-a-vis the RecBCD and AddAB clades of bacterial DSB-resecting motor nucleases.

Structures and single-molecule analysis of bacterial motor nuclease AdnAB illuminate the mechanism of DNA double-strand break resection.,Jia N, Unciuleac MC, Xue C, Greene EC, Patel DJ, Shuman S Proc Natl Acad Sci U S A. 2019 Nov 18. pii: 1913546116. doi:, 10.1073/pnas.1913546116. PMID:31740608^[1]

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