Binds the phosphorylated C-terminal domain (CTD) of the largest subunit of RNA polymerase II and functions as a scaffold for RNA processing machineries (Probable). May be involved in pre-mRNA splicing (Probable). Interacts (via the WW domains) with the phosphorylated C-terminal domain of NRPB1 (via CTD domain). Expressed in roots, shoots, rosette leaves, cauline leaves, stems and flowers. Belongs to the PRPF40 family. Intron retention.