DEPENDENCE OF YEAST PRE-MESSENGER-RNA 3'-END PROCESSING ON CFT1 - A SEQUENCE HOMOLOG OF THE MAMMALIAN AAUAAA BINDING-FACTOR

3'-End formation of pre-mRNA in yeast and mammals follows a similar bu t distinct pathway. In Saccharomyces cerevisiae, the cleavage reaction can be reconstituted by two activities called cleavage factor I and I I (CFI and CFII). A CFII component, designated CFT1 (cleavage factor t wo) was identified by its sequence similarity to the AAUAAA-binding su bunit of the mammalian cleavage and polyadenylation specificity factor (CPSF), even though the AAUAAA signal sequence appears to play no rot e in yeast pre-mRNA 3' processing. Depletion of a yeast whole-cell ext ract with antibodies to CFT1 protein abolished cleavage and polyadenyl ation of pre-mRNAs, Addition of CFII restored cleavage activity, but n ot polyadenylation. Polyadenylation required the further addition of p oly(A) polymerase and polyadenylation factor I, suggesting a close but not necessarily direct association of these two factors with the CFT1 protein.