Nuclear Pre-snRNA Export Is an Essential Quality Assurance Mechanism for Functional Spliceosomes

Cell Rep. 2019 Jun 11;27(11):3199-3214.e3. doi: 10.1016/j.celrep.2019.05.031.

Abstract

Removal of introns from pre-mRNAs is an essential step in eukaryotic gene expression, mediated by spliceosomes that contain snRNAs as key components. Although snRNAs are transcribed in the nucleus and function in the same compartment, all except U6 shuttle to the cytoplasm. Surprisingly, the physiological relevance for shuttling is unclear, in particular because the snRNAs in Saccharomyces cerevisiae were reported to remain nuclear. Here, we show that all yeast pre-snRNAs including U6 undergo a stepwise maturation process after nuclear export by Mex67 and Xpo1. Sm- and Lsm-ring attachment occurs in the cytoplasm and is important for the snRNA re-import, mediated by Cse1 and Mtr10. Finally, nuclear pre-snRNA cleavage and trimethylation of the 5'-cap finalizes shuttling. Importantly, preventing pre-snRNAs from being exported or processed results in faulty spliceosome assembly and subsequent genome-wide splicing defects. Thus, pre-snRNA export is obligatory for functional splicing and resembles an essential evolutionarily conserved quality assurance step.

Keywords: Cse1; Mex67; Mtr10; RNA processing; RNA quality control; U6; Xpo1/Crm1; mRNA; ncRNA export; snRNA; splicing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Karyopherins / genetics
  • Karyopherins / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Nucleocytoplasmic Transport Proteins / genetics
  • Nucleocytoplasmic Transport Proteins / metabolism
  • RNA Transport*
  • RNA, Small Nuclear / genetics
  • RNA, Small Nuclear / metabolism*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Spliceosomes / metabolism*

Substances

  • CSE1 protein, S cerevisiae
  • Karyopherins
  • MEX67 protein, S cerevisiae
  • MTR10 protein, S cerevisiae
  • Nuclear Proteins
  • Nucleocytoplasmic Transport Proteins
  • RNA, Small Nuclear
  • RNA-Binding Proteins
  • Receptors, Cytoplasmic and Nuclear
  • Saccharomyces cerevisiae Proteins
  • U6 small nuclear RNA
  • exportin 1 protein