7ubk
Transcription antitermination factor Qlambda, type-II crystal
Structural highlights
FunctionREGQ_LAMBD Positively regulates expression of the phage early and late gene operons. Bacterial host RNA polymerase modified by antitermination proteins transcribes through termination sites that otherwise prevent expression of the regulated genes. Publication Abstract from PubMedLambdoid bacteriophage Q proteins are transcription antipausing and antitermination factors that enable RNA polymerase (RNAP) to read through pause and termination sites. Q proteins load onto RNAP engaged in promoter-proximal pausing at a Q binding element (QBE) and adjacent sigma-dependent pause element to yield a Q-loading complex, and they translocate with RNAP as a pausing-deficient, termination-deficient Q-loaded complex. In previous work, we showed that the Q protein of bacteriophage 21 (Q21) functions by forming a nozzle that narrows and extends the RNAP RNA-exit channel, preventing formation of pause and termination RNA hairpins. Here, we report atomic structures of four states on the pathway of antitermination by the Q protein of bacteriophage lambda (Qlambda), a Q protein that shows no sequence similarity to Q21 and that, unlike Q21, requires the transcription elongation factor NusA for efficient antipausing and antitermination. We report structures of Qlambda, the Qlambda-QBE complex, the NusA-free pre-engaged Qlambda-loading complex, and the NusA-containing engaged Qlambda-loading complex. The results show that Qlambda, like Q21, forms a nozzle that narrows and extends the RNAP RNA-exit channel, preventing formation of RNA hairpins. However, the results show that Qlambda has no three-dimensional structural similarity to Q21, employs a different mechanism of QBE recognition than Q21, and employs a more complex process for loading onto RNAP than Q21, involving recruitment of Qlambda to form a pre-engaged loading complex, followed by NusA-facilitated refolding of Qlambda to form an engaged loading complex. The results establish that Qlambda and Q21 are not structural homologs and are solely functional analogs. In transcription antitermination by Qlambda, NusA induces refolding of Qlambda to form a nozzle that extends the RNA polymerase RNA-exit channel.,Yin Z, Bird JG, Kaelber JT, Nickels BE, Ebright RH Proc Natl Acad Sci U S A. 2022 Aug 16;119(33):e2205278119. doi:, 10.1073/pnas.2205278119. Epub 2022 Aug 11. PMID:35951650[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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