The function of PAB1 in translation and in PUF3 dependent deadenylation
The involvement of the poly(A)-binding protein (PAB1) in deadenylation and translation is well known. How PAB1 inhibits deadenylation and promotes translation is not well understood. I have analyzed PAB1 variants, containing entire domain deletions and substitutions of yeast residues with human residues. Chapter I discusses and provides in vivo translation rates of strains containing PAB1 variants, defects in mRNA degradation proteins, and defects in translation components. In chapter II, I address the role of PAB1 in regulated deadenylation. For this analysis I studied the effect of PUF3, a member of the PUF family of proteins that bind specific 3' UTR sequences and accelerate deadenylation and/or repress translation of the target transcript. The mechanism for PUF mediated deadenylation has recently been shown to involve recruitment of CCR4 via CAF1, suggesting PUF proteins accelerate deadenylation by increasing the local concentration of deadenylases around the mRNA. Since PUF proteins are involved in repression of translation it has been suggested that they also accelerate deadenylation through perturbation of the mRNP complex. In this work I show that PUP requires the PAB1 RRM1 domain for deadenylation of COX17 mRNA. Additionally, I show that PUP bypasses the requirement of the PAB1 P domain for deadenylation, and is required for acceleration of deadenylation through defects in the cap binding protein, elF4E. This suggests that PUP interacts with PAB1 to disturb the mRNP complex to accelerate deadenylation of COX17 mRNA.
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