Poster abstracts

Poster number 77 submitted by Jenna Smith

Characterization of the mRNP unique to substrates of the nonsense-mediated mRNA decay pathway

Jenna E. Smith (Center for RNA Molecular Biology, Case Western Reserve University), Kristian E. Baker (Center for RNA Molecular Biology, Case Western Reserve University)

Abstract:
mRNA quality control mechanisms in eukaryotes ensure fidelity of gene expression and are critical for normal cellular activity. One of the most thoroughly investigated of such mechanisms, the nonsense-mediated mRNA decay (NMD) pathway, recognizes and promotes the accelerated degradation of mRNAs containing a nonsense or premature translation termination codon (PTC), thereby guarding against the accumulation of truncated polypeptides in cells. The molecular mechanism underlying the discrimination of PTC-containing mRNAs from normal mRNAs remains to be clearly established. A prevailing model for NMD postulates that translation termination is perceived as premature if it occurs distally from the mRNA poly(A) tail and its binding protein [poly(A) binding protein, PAB1], such that PAB1 can no longer promote efficient translation termination thereby allowing the NMD machinery to be recruited to the mRNA. This model is supported by observations that 5’-proximal PTCs lead to more efficient targeting of mRNA to NMD, and that tethering PAB1 proximal to a PTC rescues the mRNA from being targeted to NMD. In contrast, however, it has been shown that in yeast, Pab1p is dispensable for NMD substrate recognition, suggesting that additional factors must be important in defining a translation termination event as premature. A critical goal for understanding how NMD substrates are recognized will be to determine the specific features of a PTC-containing mRNA and its bound proteins (i.e. the mRNP) that are important in signaling to the cellular NMD machinery that translation termination is premature. We are purifying an NMD mRNP as a means to identify and characterize such features important for targeting the mRNA to the NMD pathway. Importantly, NMD is a conserved quality control pathway in all eukaryotes, and our work in the budding yeast model Saccharomyces cerevisiae will provide insights into NMD substrate recognition in metazoa, including humans.

Keywords: NMD, mRNA decay, mRNP purification