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Early transcription elongation state of influenza A/H7N9 backtracked polymerase with singly incoporated T1106 at the U +1 position
Structural highlights
FunctionM9TI86_9INFA Plays an essential role in viral RNA transcription and replication by forming the heterotrimeric polymerase complex together with PB1 and PB2 subunits. The complex transcribes viral mRNAs by using a unique mechanism called cap-snatching. It consists in the hijacking and cleavage of host capped pre-mRNAs. These short capped RNAs are then used as primers for viral mRNAs. The PB2 subunit is responsible for the binding of the 5' cap of cellular pre-mRNAs which are subsequently cleaved after 10-13 nucleotides by the PA subunit that carries the endonuclease activity.[HAMAP-Rule:MF_04063][SAAS:SAAS00956500] Publication Abstract from PubMedThe antiviral pseudo-base T705 and its de-fluoro analog T1106 mimic adenine or guanine and can be competitively incorporated into nascent RNA by viral RNA-dependent RNA polymerases. Although dispersed, single pseudo-base incorporation is mutagenic, consecutive incorporation causes polymerase stalling and chain termination. Using a template encoding single and then consecutive T1106 incorporation four nucleotides later, we obtained a cryogenic electron microscopy structure of stalled influenza A/H7N9 polymerase. This shows that the entire product-template duplex backtracks by 5 nt, bringing the singly incorporated T1106 to the +1 position, where it forms an unexpected T1106:U wobble base pair. Similar structures show that influenza B polymerase also backtracks after consecutive T1106 incorporation, regardless of whether prior single incorporation has occurred. These results give insight into the unusual mechanism of chain termination by pyrazinecarboxamide base analogs. Consecutive incorporation destabilizes the proximal end of the product-template duplex, promoting irreversible backtracking to a more energetically favorable overall configuration. Direct observation of backtracking by influenza A and B polymerases upon consecutive incorporation of the nucleoside analog T1106.,Kouba T, Dubankova A, Drncova P, Donati E, Vidossich P, Speranzini V, Pflug A, Huchting J, Meier C, De Vivo M, Cusack S Cell Rep. 2023 Jan 31;42(1):111901. doi: 10.1016/j.celrep.2022.111901. Epub 2023 , Jan 2. PMID:36596301[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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