THE FIP1 GENE ENCODES A COMPONENT OF A YEAST PRE-MESSENGER-RNA POLYADENYLATION FACTOR THAT DIRECTLY INTERACTS WITH POLY(A) POLYMERASE

We have identified an essential gene, called FIP1, encoding a 327 amin o acid protein interacting with yeast poly(A) polymerase (PAP1) in the two-hybrid assay, Recombinant FIP1 protein forms a 1:1 complex with P AP1 in vitro. At 37 degrees C, a thermosensitive allele of FIP1 shows a shortening of poly(A) tails and a decrease in the steady-state level of actin transcripts. When assayed for 3'-end processing in vitro, fi p1 mutant extracts exhibit normal cleavage activity, but fail to polya denylate the upstream cleavage product. Polyadenylation activity is re stored by adding polyadenylation factor I (PF I). Antibodies directed against FIP1 specifically recognize a polypeptide in these fractions. Coimmunoprecipitation experiments reveal that RNA14, a subunit of clea vage factor I (CF I), directly interacts with FIP1, but not with PAP1, We propose a model in which PF I tethers PAP1 to CF I, thereby confer ring specificity to poly(A) polymerase for pre-mRNA substrates.