PBP1P, A FACTOR INTERACTING WITH SACCHAROMYCES-CEREVISIAE POLY(A)-BINDING PROTEIN, REGULATES POLYADENYLATION

The poly(A) tail of an mRNA is believed to influence the initiation of translation, and the rate at which the poly(A) tail is removed is tho ught to determine how fast an mRNA is degraded, One key factor associa ted with this 3'-end structure is the poly(A)-binding protein (Pab1p) encoded by the PAB1 gene in Saccharomyces cerevisiae, In an effort to learn more about the functional role of this protein, we used a two-hy brid screen to determine the factor(s) with which it interacts. We ide ntified five genes encoding factors that specifically interact with th e carboxy terminus of Pab1p, Of a total of 44 specific clones identifi ed, PBP1 (for Pab1p-binding protein) was isolated 38 times. Of the put ative interacting genes examined, PBP1 promoted the highest level of r esistance to 3-aminotriazole (>100 mM) in constructs in which HIS3 was used as a reporter. We determined that a fraction Of Pbp1p cosediment s with polysomes in sucrose gradients and that its distribution is ver y similar to that of Pab1p, Disruption of PBP1 showed that it is not e ssential for viability but can suppress the lethality associated with a PAB1 deletion. The suppression of pab1 Delta by pbp1 Delta appears t o be different from that mediated by other pab1 suppressors, since dis ruption of PBP1 does not alter translation rates, affect accumulation of ribosomal subunits, change mRNA poly(A) tail lengths, or result in a defect in mRNA decay, Rather, Pbp1p appears to function in the nucle us to promote proper polyadenylation, In the absence of Pbp1p, 3' term ini of pre-mRNAs are properly cleaved but lack full-length poly(A) tai ls. These effects suggest that Pbp1p may act to repress the ability of Pab1p to negatively regulate polyadenylation.