RNA helicases play fundamental roles in modulating RNA structures and facilitating RNA-protein (RNP) complex assembly in vivo. Previously, our laboratory demonstrated that the DEAD-box RNA helicase Dbp2 in Saccharomyces cerevisiae is required to promote efficient assembly of the co-transcriptionally associated mRNA-binding proteins Yra1, Nab2, and Mex67 onto poly(A)(+)RNA. We also found that Yra1 associates directly with Dbp2 and functions as an inhibitor of Dbp2-dependent duplex unwinding, suggestive of a cycle of unwinding and inhibition by Dbp2. To test this, we undertook a series of experiments to shed light on the order of events for Dbp2 in co-transcriptional mRNP assembly. We now show that Dbp2 is recruited to chromatin via RNA and forms a large, RNA-dependent complex with Yra1 and Mex67. Moreover, single-molecule fluorescence resonance energy transfer and bulk biochemical assays show that Yra1 inhibits unwinding in a concentration-dependent manner by preventing the association of Dbp2 with single-stranded RNA. This inhibition prevents over-accumulation of Dbp2 on mRNA and stabilization of a subset of RNA polymerase II transcripts. We propose a model whereby Yra1 terminates a cycle of mRNP assembly by Dbp2.

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Journal Article | Research Support, N.I.H., Extramural | Research Support, Non-U.S. Gov't

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Ma WK, Paudel BP, Xing Z, Sabath IG, Rueda D, Tran EJ

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