1
|
Gao F, Ye F, Zhang B, Cronin N, Buck M, Zhang X. Structural basis of σ 54 displacement and promoter escape in bacterial transcription. Proc Natl Acad Sci U S A 2024; 121:e2309670120. [PMID: 38170755 PMCID: PMC10786286 DOI: 10.1073/pnas.2309670120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 11/17/2023] [Indexed: 01/05/2024] Open
Abstract
Gene transcription is a fundamental cellular process carried out by RNA polymerase (RNAP). Transcription initiation is highly regulated, and in bacteria, transcription initiation is mediated by sigma (σ) factors. σ recruits RNAP to the promoter DNA region, located upstream of the transcription start site (TSS) and facilitates open complex formation, where double-stranded DNA is opened up into a transcription bubble and template strand DNA is positioned inside RNAP for initial RNA synthesis. During initial transcription, RNAP remains bound to σ and upstream DNA, presumably with an enlarging transcription bubble. The release of RNAP from upstream DNA is required for promoter escape and processive transcription elongation. Bacteria sigma factors can be broadly separated into two classes with the majority belonging to the σ70 class, represented by the σ70 that regulates housekeeping genes. σ54 forms a class on its own and regulates stress response genes. Extensive studies on σ70 have revealed the molecular mechanisms of the σ70 dependent process while how σ54 transitions from initial transcription to elongation is currently unknown. Here, we present a series of cryo-electron microscopy structures of the RNAP-σ54 initial transcribing complexes with progressively longer RNA, which reveal structural changes that lead to promoter escape. Our data show that initially, the transcription bubble enlarges, DNA strands scrunch, reducing the interactions between σ54 and DNA strands in the transcription bubble. RNA extension and further DNA scrunching help to release RNAP from σ54 and upstream DNA, enabling the transition to elongation.
Collapse
Affiliation(s)
- Forson Gao
- Section of Structural and Synthetic Biology, Department of Infectious Disease, Imperial College London, LondonSW7 2AZ, United Kingdom
| | - Fuzhou Ye
- Section of Structural and Synthetic Biology, Department of Infectious Disease, Imperial College London, LondonSW7 2AZ, United Kingdom
| | - Bowen Zhang
- Section of Structural and Synthetic Biology, Department of Infectious Disease, Imperial College London, LondonSW7 2AZ, United Kingdom
| | - Nora Cronin
- London Consortium for High Resolution cryoEM, the Francis Crick Institute, LondonNW1 1AT, United Kingdom
| | - Martin Buck
- Department of Life Sciences, Imperial College London, LondonSW7 2AZ, United Kingdom
| | - Xiaodong Zhang
- Section of Structural and Synthetic Biology, Department of Infectious Disease, Imperial College London, LondonSW7 2AZ, United Kingdom
- DNA processing machines laboratory, the Francis Crick Institute, LondonNW1 1AT, United Kingdom
| |
Collapse
|
2
|
Chen H, Gu Z, Yang L, Liu F, An R, Ge Y, Liang X. Direct dsRNA preparation by promoter-free RCT and RNase H cleavage using one circular dsDNA template with a mismatched bubble. RNA (NEW YORK, N.Y.) 2023; 29:1691-1702. [PMID: 37536954 PMCID: PMC10578470 DOI: 10.1261/rna.079670.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2023] [Accepted: 07/13/2023] [Indexed: 08/05/2023]
Abstract
Double-stranded RNA (dsRNA) has aroused widespread interest due to its effects on immunity and applications based on RNAi. However, the in vitro preparation of dsRNA is costly and laborious. In this study, we have developed a novel and interesting method designated as pfRCT (promoter-free rolling-circle transcription) for direct, facile, and efficient dsRNA preparation. This method generates equal amounts of sense and antisense strands simultaneously from a single circular dsDNA template. To initiate transcription by T7 RNA polymerase without directional preference, a 9-15-bp bubble (mismatched duplex with strong sequence symmetry) is introduced into the template. During RCT, all the necessary reagents, including the template, NTPs, RNA polymerase, RNase H, and Helpers, are present in one pot; and the just-transcribed RNA is immediately truncated by RNase H to monomers with the desired size. The ends of the dsRNA product can also be simply sealed by T4 RNA ligase 1 after pfRCT. This new approach is expected to promote the applications of dsRNA.
Collapse
Affiliation(s)
- Hui Chen
- College of Food Science and Engineering, Ocean University of China, Qingdao 266550, Shandong, China
- Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266235, Shandong, China
| | - Zhenzhu Gu
- College of Food Science and Engineering, Ocean University of China, Qingdao 266550, Shandong, China
| | - Liu Yang
- Department of Biochemistry and Molecular Biology School of Basic Medicine, Qingdao University, Qingdao 266071, Shandong, China
| | - Feng Liu
- College of Food Science and Engineering, Ocean University of China, Qingdao 266550, Shandong, China
| | - Ran An
- College of Food Science and Engineering, Ocean University of China, Qingdao 266550, Shandong, China
- Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266235, Shandong, China
| | - Yinlin Ge
- Department of Biochemistry and Molecular Biology School of Basic Medicine, Qingdao University, Qingdao 266071, Shandong, China
| | - Xingguo Liang
- College of Food Science and Engineering, Ocean University of China, Qingdao 266550, Shandong, China
- Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266235, Shandong, China
| |
Collapse
|
3
|
The Context-Dependent Influence of Promoter Sequence Motifs on Transcription Initiation Kinetics and Regulation. J Bacteriol 2021; 203:JB.00512-20. [PMID: 33139481 DOI: 10.1128/jb.00512-20] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The fitness of an individual bacterial cell is highly dependent upon the temporal tuning of gene expression levels when subjected to different environmental cues. Kinetic regulation of transcription initiation is a key step in modulating the levels of transcribed genes to promote bacterial survival. The initiation phase encompasses the binding of RNA polymerase (RNAP) to promoter DNA and a series of coupled protein-DNA conformational changes prior to entry into processive elongation. The time required to complete the initiation phase can vary by orders of magnitude and is ultimately dictated by the DNA sequence of the promoter. In this review, we aim to provide the required background to understand how promoter sequence motifs may affect initiation kinetics during promoter recognition and binding, subsequent conformational changes which lead to DNA opening around the transcription start site, and promoter escape. By calculating the steady-state flux of RNA production as a function of these effects, we illustrate that the presence/absence of a consensus promoter motif cannot be used in isolation to make conclusions regarding promoter strength. Instead, the entire series of linked, sequence-dependent structural transitions must be considered holistically. Finally, we describe how individual transcription factors take advantage of the broad distribution of sequence-dependent basal kinetics to either increase or decrease RNA flux.
Collapse
|