The in vivo kinetics of RNA polymerase II elongation during co-transcriptional splicing

PLoS Biol. 2011 Jan 11;9(1):e1000573. doi: 10.1371/journal.pbio.1000573.

Abstract

RNA processing events that take place on the transcribed pre-mRNA include capping, splicing, editing, 3' processing, and polyadenylation. Most of these processes occur co-transcriptionally while the RNA polymerase II (Pol II) enzyme is engaged in transcriptional elongation. How Pol II elongation rates are influenced by splicing is not well understood. We generated a family of inducible gene constructs containing increasing numbers of introns and exons, which were stably integrated in human cells to serve as actively transcribing gene loci. By monitoring the association of the transcription and splicing machineries on these genes in vivo, we showed that only U1 snRNP localized to the intronless gene, consistent with a splicing-independent role for U1 snRNP in transcription. In contrast, all snRNPs accumulated on intron-containing genes, and increasing the number of introns increased the amount of spliceosome components recruited. This indicates that nascent RNA can assemble multiple spliceosomes simultaneously. Kinetic measurements of Pol II elongation in vivo, Pol II ChIP, as well as use of Spliceostatin and Meayamycin splicing inhibitors showed that polymerase elongation rates were uncoupled from ongoing splicing. This study shows that transcription elongation kinetics proceed independently of splicing at the model genes studied here. Surprisingly, retention of polyadenylated mRNA was detected at the transcription site after transcription termination. This suggests that the polymerase is released from chromatin prior to the completion of splicing, and the pre-mRNA is post-transcriptionally processed while still tethered to chromatin near the gene end.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Fluorescence Recovery After Photobleaching
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Introns
  • Inverted Repeat Sequences
  • Lac Repressors / genetics
  • Lac Repressors / metabolism
  • RNA Polymerase II / metabolism*
  • RNA Precursors / metabolism*
  • RNA Splicing*
  • RNA, Messenger / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Ribonucleoproteins, Small Nuclear / genetics
  • Ribonucleoproteins, Small Nuclear / metabolism
  • Spliceosomes / metabolism
  • Transcription, Genetic*
  • Tumor Cells, Cultured
  • beta-Globins / genetics

Substances

  • Lac Repressors
  • RNA Precursors
  • RNA, Messenger
  • Recombinant Fusion Proteins
  • Ribonucleoproteins, Small Nuclear
  • beta-Globins
  • Green Fluorescent Proteins
  • RNA Polymerase II