One of the multiple factors required for polyadenylation and 3'-end cleavage of pre-mRNAs (By similarity). Required for the targeted 3' processing of antisense transcripts that triggers transcriptional silencing of the corresponding sense gene (PubMed:19965720). Homodimer. Belongs to the CSTF complex (By similarity). Forms a complex with cleavage and polyadenylation specificity factor (CPSF) subunits CPSF30, CSTF64, PCFS1, PCFS5 and FIPS5 (PubMed:12379796, PubMed:16282318, PubMed:18479511, PubMed:18221017, PubMed:20214900). Impaired antisense-RNA-mediated gene silencing (e.g. suppression of overexpression of FCA-mediated FLC repression). Delayed flowering and female gametophytic lethality.