Required for endonucleolytic cleavage during polyadenylation-dependent pre-mRNA 3'-end formation. Component of a pre-mRNA cleavage factor complex. Interacts directly with PCF11. Belongs to the Clp1 family. Clp1 subfamily. May lack the polyribonucleotide 5'-hydroxyl-kinase and polynucleotide 5'-hydroxyl-kinase activities that are characteristic of the human ortholog.