The role of deadenylation in the degradation of unstable mRNAs in trypanosomes

Nucleic Acids Res. 2009 Sep;37(16):5511-28. doi: 10.1093/nar/gkp571. Epub 2009 Jul 13.

Abstract

Removal of the poly(A) tail is the first step in the degradation of many eukaryotic mRNAs. In metazoans and yeast, the Ccr4/Caf1/Not complex has the predominant deadenylase activity, while the Pan2/Pan3 complex may trim poly(A) tails to the correct size, or initiate deadenylation. In trypanosomes, turnover of several constitutively-expressed or long-lived mRNAs is not affected by depletion of the 5'-3' exoribonuclease XRNA, but is almost completely inhibited by depletion of the deadenylase CAF1. In contrast, two highly unstable mRNAs, encoding EP procyclin and a phosphoglycerate kinase, PGKB, accumulate when XRNA levels are reduced. We here show that degradation of EP mRNA was partially inhibited after CAF1 depletion. RNAi-targeting trypanosome PAN2 had a mild effect on global deadenylation, and on degradation of a few mRNAs including EP. By amplifying and sequencing degradation intermediates, we demonstrated that a reduction in XRNA had no effect on degradation of a stable mRNA encoding a ribosomal protein, but caused accumulation of EP mRNA fragments that had lost substantial portions of the 5' and 3' ends. The results support a model in which trypanosome mRNAs can be degraded by at least two different, partially independent, cytoplasmic degradation pathways attacking both ends of the mRNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cytoplasm / enzymology
  • Genome, Protozoan
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism
  • Phosphoglycerate Kinase / genetics
  • Phosphoglycerate Kinase / metabolism
  • Protozoan Proteins / antagonists & inhibitors
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism
  • Protozoan Proteins / physiology*
  • RNA Interference
  • RNA Stability*
  • RNA, Messenger / chemistry
  • RNA, Messenger / metabolism*
  • Ribonucleases / antagonists & inhibitors
  • Ribonucleases / genetics
  • Ribonucleases / physiology*
  • Trypanosoma / enzymology*
  • Trypanosoma / genetics
  • Trypanosoma / growth & development

Substances

  • EP procyclin protein, Trypanosoma brucei
  • Membrane Glycoproteins
  • Protozoan Proteins
  • RNA, Messenger
  • Phosphoglycerate Kinase
  • Ribonucleases
  • mRNA deadenylase