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CRYO-EM STRUCTURE OF HUMAN U7 SNRNP WITH METHYLATED noncleavable H2A* SUBSTRATE PRE-MRNA (FOCUS MAP)
Structural highlights
FunctionCPSF3_HUMAN Component of the cleavage and polyadenylation specificity factor (CPSF) complex that play a key role in pre-mRNA 3'-end formation, recognizing the AAUAAA signal sequence and interacting with poly(A) polymerase and other factors to bring about cleavage and poly(A) addition. Has endonuclease activity, and functions as mRNA 3'-end-processing endonuclease. Also involved in the histone 3'-end pre-mRNA processing. U7 snRNP-dependent protein that induces both the 3'-endoribonucleolytic cleavage of histone pre-mRNAs and acts as a 5' to 3' exonuclease for degrading the subsequent downstream cleavage product (DCP) of mature histone mRNAs. Cleavage occurs after the 5'-ACCCA-3' sequence in the histone pre-mRNA leaving a 3'hydroxyl group on the upstream fragment containing the stem loop (SL) and 5' phosphate on the downstream cleavage product (DCP) starting with CU nucleotides. The U7-dependent 5' to 3' exonuclease activity is processive and degrades the DCP RNA substrate even after complete removal of the U7-binding site. Binds to the downstream cleavage product (DCP) of histone pre-mRNAs and the cleaved DCP RNA substrate in a U7 snRNP dependent manner.[1] [2] [3] [4] Publication Abstract from PubMedThe U7 snRNP (small nuclear ribonucleoprotein) is responsible for the 3'-end processing of replication-dependent histone messenger RNA precursors (pre-mRNAs). A helix in the Lsm11 N-terminal extension contacts the metallo-beta-lactamase domain of the U7 snRNP endonuclease CPSF73. We mutated or deleted this helix and found that the mutant machineries had substantially reduced cleavage activity toward the pre-mRNA. Our cryo-electron microscopy (cryo-EM) studies indicated that the helix was important for helping to hold CPSF73 in its correct position for the cleavage reaction. We also reconstituted a wild-type U7 snRNP in complex with a methylated, noncleavable pre-mRNA. We observed that CPSF73 could achieve an open conformation independent of RNA binding to its active site. Finally, we found that a previously uninterpreted EM density for a small helix at the CPSF73-CPSF100 interface belonged to the C-terminal end of CstF77, copurified from insect cells and highly conserved among CstF77 homologs. This CstF77 binding site had a small effect on the cleavage activity of U7 snRNP. Overall, our studies have revealed the importance of the conserved helix in the Lsm11 N-terminal extension for U7 snRNP, provided structural evidence that CPSF73 can achieve an open, active conformation without RNA binding in its active site, and identified a previously unknown binding site for CstF77 in CPSF100. An N-terminal helix of Lsm11 stabilizes CPSF73 in U7 snRNP for histone pre-mRNA 3'-end processing.,Desotell A, Marzluff WF, Dominski Z, Tong L Nucleic Acids Res. 2026 Jan 5;54(1):gkaf1442. doi: 10.1093/nar/gkaf1442. PMID:41495886[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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