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The exon junction complex is detected on CBP80-bound but not eIF4E-bound mRNA in mammalian cells: dynamics of mRNP

Fabrice Lejeune1, Yasuhito Ishigaki, Xiaojie Li

  • 1Department of Biochemistry and Biophysics, School of Medicine and Dentistry, 601 Elmwood Avenue, Box 712, University of Rochester, Rochester, NY 14642, USA.

The EMBO Journal
|July 3, 2002
PubMed

Insights

Newly spliced mRNAs recruit proteins involved in nonsense-mediated mRNA decay (NMD). Research shows nuclear CBP80 binds intron-containing RNA, unlike nuclear eIF4E, impacting mRNA processing and export.

Area of Science:

  • Molecular Biology
  • RNA Biology
  • Cell Biology

Background:

  • Newly spliced mRNAs in mammalian cells feature exon-exon junction complexes.
  • These complexes recruit Upf3 and Upf2 proteins, crucial for nonsense-mediated mRNA decay (NMD).
  • Upf proteins associate with mRNA bound by nuclear CBP80/CBP20, but not cytoplasmic eIF4E.

Purpose of the Study:

  • To investigate the role of nuclear cap-binding proteins in mRNA processing and NMD.
  • To determine if nuclear eIF4E binds nascent, non-productive transcripts.
  • To characterize the association of NMD factors with CBP80-bound versus eIF4E-bound mRNA in the nucleus and cytoplasm.

Main Methods:

  • Detection of proteins associated with specific mRNA populations using biochemical assays.
  • Analysis of nuclear and cytoplasmic fractions to track protein localization.
  • Investigating the binding of RNA polymerase II and intron-containing RNA to cap-binding proteins.

Main Results:

  • Nuclear CBP80, but not nuclear eIF4E, is found with intron-containing RNA and RNA polymerase II.
  • Proteins including RNPS1, Y14, SRm160, REF/Aly, TAP, Upf3X, and Upf2 are associated with nuclear CBP80-bound mRNA.
  • These proteins remain associated with CBP80-bound mRNA after export to the cytoplasm.

Conclusions:

  • Nuclear CBP80 plays a role in binding intron-containing RNA and interacting with the transcription machinery.
  • The NMD machinery and associated proteins are recruited to CBP80-bound mRNA in the nucleus.
  • These findings suggest a coordinated process of mRNA processing, nuclear export, and potential NMD targeting involving CBP80-bound transcripts.

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