Component of the cap-binding complex (CBC), which binds cotranscriptionally to the 5'-cap of pre-mRNAs and is involved in various processes such as pre-mRNA splicing and RNA-mediated gene silencing (RNAi) by microRNAs (miRNAs). The CBC complex is involved in miRNA-mediated RNA interference and is required for primary miRNA processing. In the CBC complex, ABH1/CBP80 does not bind directly capped RNAs (m7GpppG-capped RNA) but is required to stabilize the movement of the N-terminal loop of CBP20 and lock the CBC into a high affinity cap-binding state with the cap structure (By similarity). Component of the nuclear cap-binding complex (CBC), a heterodimer composed of ABH1/CBP80 and CBP20 that interacts with m7GpppG-capped RNA. Predominantly nuclear. Belongs to the NCBP1 family.