The major pathways of mRNA turnover in eukaryotes initiate with shortening of the polyA tail. CAF1 encodes a critical component of the major cytoplasmic deadenylase in yeast. Both Caf1p is required for normal mRNA deadenylation in vivo and localizes to the cytoplasm. Caf1p copurifies with a Ccr4p-dependent polyA-specific exonuclease activity. Some members of this family include and inserted RNA binding domain pfam01424. This family of proteins is related to other exonucleases pfam00929 (Bateman A pers. obs.). The crystal structure of Saccharomyces cerevisiae Pop2 has been resolved at 2.3 Angstrom resolution.