期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：3
DOI：10.1073/pnas.2114065119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Hairpin pyrrole-imidazole (Py-Im) polyamides can be programmed to bind a broad repertoire of DNA sequences. Py-Im small molecules can be used to target cancer-specific coding regions and block transcription elongation. This transcription blockage by Py-Im cannot be rescued by transcription elongation factors, such as TFIIS. The mechanism by which Py-Im blocks transcription remains elusive. To understand the structural basis of this strong transcription blockage, we solved five different structures containing an eight-ring hairpin Py-Im bound with either a Pol II elongation complex (EC) or a DNA duplex. These structures revealed that Py-Im can trap Pol II EC in a treadmill-like manner. This knowledge may pave the way for the development of small molecules that inhibit transcriptional addiction in cancer.
Elongating RNA polymerase II (Pol II) can be paused or arrested by a variety of obstacles. These obstacles include DNA lesions, DNA-binding proteins, and small molecules. Hairpin pyrrole-imidazole (Py-Im) polyamides bind to the minor groove of DNA in a sequence-specific manner and induce strong transcriptional arrest. Remarkably, this Py-Im–induced Pol II transcriptional arrest is persistent and cannot be rescued by transcription factor TFIIS. In contrast, TFIIS can effectively rescue the transcriptional arrest induced by a nucleosome barrier. The structural basis of Py-Im–induced transcriptional arrest and why TFIIS cannot rescue this arrest remain elusive. Here we determined the X-ray crystal structures of four distinct Pol II elongation complexes (Pol II ECs) in complex with hairpin Py-Im polyamides as well as of the hairpin Py-Im polyamides–dsDNA complex. We observed that the Py-Im oligomer directly interacts with RNA Pol II residues, introduces compression of the downstream DNA duplex, prevents Pol II forward translocation, and induces Pol II backtracking. These results, together with biochemical studies, provide structural insight into the molecular mechanism by which Py-Im blocks transcription. Our structural study reveals why TFIIS fails to promote Pol II bypass of Py-Im–induced transcriptional arrest.
