Accepted post-doctoral position at University of North Carolina after receiving PhD
Now employed as Academic Editor and Academic Illustrator at Research Square, Durham, NC
Most eukaryotic mRNAs possess a 5′ cap at their 5′ ends and a poly(A) tail at their 3′ ends. It is generally thought that these structures play important roles in gene expression. For example, it is believed that a transcript must possess a poly(A) tail, and possibly a 5′ cap, in order to leave the nucleus. Additionally, both of these structures have been demonstrated to play important roles in translation and in transcript stability.
Much of what we know about the roles of the cap and poly(A) tail comes from experiments using cell extracts, exogenous mRNA electroporated into cells, or analyses performed with very unhealthy mutant cells, all of which may not imitate what occurs in vivo. To circumvent these issues, I have made reporter constructs that are transcribed in a wild type yeast cell then cleaved. I have demonstrated that 5′ unadenylated cleavage products can be translated, but are rapidly targeted to the cytoplasmic exosome for degradation. In accordance with the cap being required for translation and transcript stability, uncapped 3′ cleavage products are extremely unstable and are not translated.
This approach was then utilized to test the proposed requirement of the poly(A) tail in recognition of premature termination codons by the nonsense-mediated decay pathway. Contrary to what was believed, unadenylated nonsense transcripts are still recognized as nonsense. This indicates that the distance between a premature termination codon and the poly(A) tail is not a critical determinant for nonsense-mediated decay in yeast.
Another set of studies has used reporter transcripts that contain cleavage sites for the nuclear endonuclease, Rnt1p. These constructs have been used to study the requirement of the 5′ cap and poly(A) tail for mRNA export. Contrary to what is believed, I have demonstrated that the 5′ cap and poly(A) tail are not required for export.
This work has provided new insights into many aspects of gene expression. Furthermore, the constructs that I have described should be useful for more detailed studies of the roles of the cap and poly(A) tail in all aspects of mRNA metabolism.
The role of the cap and poly(A) tail in mRNA metabolism