西亞試劑：Running in Reverse: The Structural Basis for Translocation

Running in Reverse: The Structural Basis for Translocation Polarity in Hexameric Helicases

Nathan D. Thomsen1 and James M. Berger1, ,

1 Department of Molecular and Cell Biology, Quantitative Biosciences Institute, University of California, Berkeley, CA 94720, USA

Hexameric helicases couple ATP hydrolysis to processive separation of nucleic acid duplexes, a process critical for gene expression, DNA replication, and repair. All hexameric helicases fall into two families with opposing translocation polarities: the 3′→5′ AAA+ and 5′→3′ RecA-like enzymes. To understand how a RecA-like hexameric helicase engages and translocates along substrate, we determined the structure of the E. coli Rho transcription termination factor bound to RNA and nucleotide. Interior nucleic acid-binding elements spiral around six bases of RNA in a manner unexpectedly reminiscent of an AAA+ helicase, the papillomavirus E1 protein. Four distinct ATP-binding states, representing potential catalytic intermediates, are coupled to RNA positioning through a complex allosteric network. Comparative studies with E1 suggest that RecA and AAA+ hexameric helicases use different portions of their chemomechanical cycle for translocating nucleic acid and track in opposite directions by reversing the firing order of ATPase sites around the hexameric ring.For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

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