One of the multiple factors required for polyadenylation and 3'-end cleavage of mammalian pre-mRNAs (By similarity). May be responsible for the interaction of CSTF with other factors to form a stable complex on the pre-mRNA (By similarity). Homodimer (By similarity). The CSTF complex is composed of CSTF1 (50 kDa subunit), CSTF2 (64 kDa subunit) and CSTF3 (77 kDa subunit) (By similarity). Interacts (via repeats WD) directly with CSTF3 (By similarity). Interacts (via repeat WD6) with BARD1 (By similarity). Interacts with ERCC6 (By similarity). N-terminus mediates homodimerization.