Poster abstracts

Poster number 27 submitted by Sarah Geisler

RNA decapping influences mRNA biogenesis

Sarah Geisler (Center for RNA Molecular Biology, Case Western Reserve University), Jeff Coller (Center for RNA Molecular Biology, Case Western Reserve University)

Abstract:
In this study we provide evidence that Dcp2p, the decapping enzyme which destroys mRNAs in the cytoplasm, is involved in the destruction of noncoding RNAs (ncRNAs). We have preliminary evidence suggesting that abrogation of decapping stabilizes ncRNAs ultimately resulting in transcriptional downregulation.

In the cytoplasm, mRNA turnover is initiated by the loss of the poly(A) tail, followed by decapping, and subsequent 5’-3’ exoribonuclease digestion. Blocking mRNA decapping by mutation results in dramatic stabilization of the mRNA but no apparent increase in total mRNA levels at steady-state relative to wild-type cells. We account for this discrepancy by showing that loss of decapping enzyme function results in a dramatic inhibition of nuclear mRNA transcription at the well-studied GAL loci. First, in induction assays, decapping enzyme mutants accumulate significantly less message than a wild-type cell (WT). Additionally, appropriate transcription requires the catalytic activity of the decapping enzyme. Point mutations in the catalytic domain of DCP2, dcp2-4, result in induction defects similar to the gene deletion. Second, blocking cytoplasmic decapping or decay by other extragenic mutations (i.e. mutations in decapping activators or the cytoplasmic exonuclease) does not result in aberrant transcription. Third, ncRNAs specifically at the GAL loci, which have been implicated in transcriptional regulation, show increased levels in decapping enzyme mutants. Together these data are suggestive of a novel, possibly nuclear function for the decapping enzyme in regulating mRNA transcription through the destruction of ncRNAs.

Keywords: Decapping enzyme, mRNA decay, transcription