Automated electron tomography of large nuclear RNP (lnRNP) particles - The naturally assembled complexes of precursor messenger RNA and splicing factors

Ohad Medalia, Abraham J. Koster, Ante Tocilij, Mina Angenitzki, Joseph Sperling, Ziva Berkovitch-Yellin, Ruth Sperling

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Splicing of nuclear pre-mRNA is an important step in the regulation of gene expression as only correctly spliced mRNAs will be exported to the cytoplasm to function in protein synthesis. Nuclear RNA transcripts of split genes and their splicing products, as well as the general population of nuclear polyadenylated RNA, are packaged in multicomponent large nuclear ribonucleoprotein (lnRNP) particles. These lnRNP particles, which sediment at the 200S region in sucrose gradients, contain all U snRNPs required for pre- mRNA splicing and several protein splicing factors, including U2AF and the SR proteins and can thus be viewed as naturally assembled complexes of pre-mRNA nd splicing factors. We have previously reconstructed the three-dimensional image of negatively stained individual lnRNP particles by automated electron tomography. The reconstruction revealed a compact structure, 50 nm in diameter, composed of four major subunits. Here we further analyzed the reconstructed models and the apparent connectivity between the subunits using a new rendering technique. The uniformity of the lnRNP particles was substantiated by measurement of the volume engulfed by their surface. This study further supports the model proposed for the packaging of nuclear pre- mRNAs in lnRNP particles, where each substructure represents a functional unit. This model is compatible with the requirements for alternative splicing in multiintronic pre-mRNAs, and with the fact that the splicing of multiintronic pre-mRNAs does not occur in a sequential manner.

Original languageEnglish
Pages (from-to)228-236
Number of pages9
JournalJournal of Structural Biology
Volume120
Issue number3
DOIs
StatePublished - 1 Jan 1997
Externally publishedYes

Keywords

  • Electron microscopy
  • Electron tomography
  • Model
  • Pre-mRNA splicing
  • lnRNP particles

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