The human RNA polymerase I structure reveals an HMG-like docking domain specific to metazoans - Daiß, Julia L; Pilsl, Michael; Straub, Kristina; Bleckmann, Andrea; Höcherl, Mona; Heiss, Florian B; Abascal-Palacios, Guillermo; Ramsay, Ewan P; Tluckova, Katarina; Mars, Jean-Clement; Fürtges, Torben; Bruckmann, Astrid; et al. (Life Science Alliance, 2022)
Transcription of the ribosomal RNA precursor by RNA polymerase (Pol) I is a major determinant of cellular growth, and dysregulation is observed in many cancer types. Here, we present the purification of human Pol I from cells carrying a genomic GFP fusion on the largest subunit allowing the structural and functional analysis of the enzyme across species. In contrast to yeast, human Pol I carries a single-subunit stalk, and in vitro transcription indicates a reduced proofreading activity. Determination of the human Pol I cryo-EM reconstruction in a close-to-native state rationalizes the effects of disease-associated mutations and uncovers an additional domain that is built into the sequence of Pol I subunit RPA1. This “dock II” domain resembles a truncated HMG box incapable of DNA binding which may serve as a downstream transcription factor–binding platform in metazoans. Biochemical analysis, in situ modelling, and ChIP data indicate that Topoisomerase 2a can be recruited to Pol I via the domain and cooperates with the HMG box domain–containing factor UBF. These adaptations of the metazoan Pol I transcription system may allow efficient release of positive DNA supercoils accumulating downstream of the transcription bubble.
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Keywords: article; Health -- Toxicology and Mutagenesis -- Plant Science -- Biochemistry -- Genetics and Molecular Biology (miscellaneous) -- Ecology