One of the multiple factors required for polyadenylation and 3'-end cleavage of mammalian pre-mRNAs. This subunit is directly involved in the binding to pre-mRNAs. {ECO:0000269|PubMed:32816001, ECO:0000269|PubMed:9199325}. This is the function of CSTF2 (cleavage stimulation factor subunit 2, ENSG00000101811).