Diverse and conserved roles of the protein Ssu72 in eukaryotes: from yeast to higher organisms
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REVIEW
Diverse and conserved roles of the protein Ssu72 in eukaryotes: from yeast to higher organisms Changfu Liu1 · Weihao Zhang1 · Wenge Xing1 Received: 29 July 2020 / Revised: 4 November 2020 / Accepted: 6 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Gene transcription is a complex biological process that involves a set of factors, enzymes and nucleotides. Ssu72 plays a crucial role in every step of gene transcription. RNA polymerase II (RNAPII) occupies an important position in the synthesis of mRNAs. The largest subunit of RNAPII, Rpb1, harbors its C-terminal domain (CTD), which participates in the initiation, elongation and termination of transcription. The CTD consists of heptad repeats of the consensus motif Tyr1–Ser2–Pro3– Thr4–Ser5–Pro6–Ser7 and is highly conserved among different species. The CTD is flexible in structure and undergoes conformational changes in response to serine phosphorylation and proline isomerization, which are regulated by specific kinases/phosphatases and isomerases, respectively. Ssu72 is a CTD phosphatase with catalytic activity against phosphorylated Ser5 and Ser7. The isomerization of Pro6 affects the binding of Ssu72 to its substrate. Ssu72 can also indirectly change the phosphorylation status of Ser2. In addition, Ssu72 is a member of the 3′-end cleavage and polyadenylation factor (CPF) complex. Together with other CPF components, Ssu72 regulates the 3′-end processing of premature mRNA. Recent studies have revealed other roles of Ssu72, including its roles in balancing phosphate homeostasis and controlling chromosome behaviors, which should be further explored. In conclusion, the protein Ssu72 is an enzyme worthy of attention, not confined to its role in gene transcription. Keywords RNA polymerase II · C-terminal domain · Ssu72 · TFIIB · CPF
Introduction In the process of gene transcription, the DNA template is transcribed from the 3′-end to 5′-end, and the RNA chain is synthesized from the 5′-end to 3′-end. RNA synthesis generally consists of two steps. The first step involves synthesis of the original transcript (including the initiation, elongation and termination of transcription). The second step is a process to transform the biologically inactive pre mRNA into mature RNA with biological function. The second step, which takes place in only eukaryotes, consists of 5′-end capping; polyadenylation, which is a two-step Communicated by M. Kupiec. * Wenge Xing [email protected] 1
Department of Interventional Treatment, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Key Laboratory of Cancer Prevention and Therapy, Tianjin, Tianjin’s Clinical Research Center for Cancer, Tianjin 300060, China
reaction consisting of endonucleolytic cleavage followed by poly(A) tail synthesis; and splicing. Most splicing is cotranscriptional, as are 3′-end cleavage and polyadenylation, and 3′-end cleavage is essential for efficient termination. For some mRNAs, extra modification by methylati
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