Component of the cleavage factor IA (CF IA) complex, which is involved in the endonucleolytic cleavage during polyadenylation-dependent pre-mRNA 3'-end formation. Associates with HRB1/CF IB to form the cleavage factor I (CF I) complex. CF I is required for correct positioning of a larger protein complex, the cleavage and polyadenylation factor (CPF) complex, which contains the catalytic subunits executing mRNA cleavage and polyadenylation. CLP1 mediates interactions between CF IA and CPF factors. CLP1 is also involved in maintaining the CF IA interaction with the C-terminal domain of RNA Pol II largest subunit via PCF11, which links pre-mRNA 3'-end processing to transcription termination. Component of the cleavage factor IA (CF IA) complex, which is a heterohexameric complex with 2:2:1:1 stoichiometry of RNA14, RNA15, PCF11 and CLP1. It contains 2 copies of an RNA14-RNA15 dimer and 1 copy of CLP1-PCF11. The complex interacts with the cleavage factor HRB1/CF IB to form the cleavage factor I (CF I) complex, and binds to RNA. Interacts directly with PCF11. Interacts with the CPF components CFT1, PTA1, PFS2, YSH1 and SSU72. Causes defective 3'-end formation and transcriptional read-through. 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.