Sequence Similarity Between the 73-Kilodalton Protein of Mammalian CPSF and a Subunit of Yeast Polyadenylation Factor I

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Abstract
The 3′ ends of most eukaryotic messenger RNAs are generated by endonucleolytic cleavage and polyadenylation. In mammals, the cleavage and polyadenylation specificity factor (CPSF) plays a central role in both steps of the processing reaction. Here, the cloning of the 73-kilodalton subunit of CPSF is reported. Sequence analyses revealed that a yeast protein (Ysh1) was highly similar to the 73-kD polypeptide. Ysh1 constitutes a new subunit of polyadenylation factor I (PFI), which has a role in yeast pre-mRNA 3′-end formation. This finding was unexpected because in contrast to CPSF, PFI is only required for the polyadenylation reaction. These results contribute to the understanding of how 3′-end processing factors may have evolved.