Polyadenylation site choice in yeast is affected by competition between Npl3 and polyadenylation factor CFI

Multiple steps in mRNA processing and transcription are coupled. Notably, the processing of mRNA 39 ends is linked to transcription termination by RNA polymerase II. Previously, we found that the yeast hnRNP protein NpI3 can negatively regulate 39 end mRNA formation and termination at the GAL1 gene. Here we show that overexpression of the Hrp1 or Rna14 subunits of the CF IA polyadenylation factor increases recognition of a weakened polyadenylation site. Genetic interactions of mutant alleles of NPL3 or HRP1 with RNA15 also indicate antagonism between these factors. NpI3 competes with Rna15 for binding to a polyadenylation precursor and inhibits cleavage and polyadenylation in vitro. These results suggest that an important function of hnRNP proteins is to ensure the fidelity of mRNA processing. Our results support a model in which balanced competition of NpI3 with mRNA processing factors may promote recognition of proper polyadenylation sites while suppressing cryptic sites.