Summary information and primary citation
- PDB-id
- 7ubm; SNAP-derived features in text and JSON formats;
DNAproDB
- Class
- gene regulation, transferase-DNA-RNA
- Method
- cryo-EM (3.13 Å)
- Summary
- Transcription antitermination complex: "pre-engaged" qlambda-loading complex
- Reference
- Yin Z, Bird JG, Kaelber JT, Nickels BE, Ebright RH (2022): "In transcription antitermination by Q lambda , NusA induces refolding of Q lambda to form a nozzle that extends the RNA polymerase RNA-exit channel." Proc.Natl.Acad.Sci.USA, 119, e2205278119. doi: 10.1073/pnas.2205278119.
- Abstract
- Lambdoid 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 λ (Qλ), 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 Qλ, the Qλ-QBE complex, the NusA-free pre-engaged Qλ-loading complex, and the NusA-containing engaged Qλ-loading complex. The results show that Qλ, like Q21, forms a nozzle that narrows and extends the RNAP RNA-exit channel, preventing formation of RNA hairpins. However, the results show that Qλ 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 Qλ to form a pre-engaged loading complex, followed by NusA-facilitated refolding of Qλ to form an engaged loading complex. The results establish that Qλ and Q21 are not structural homologs and are solely functional analogs.
