Binds the phosphorylated C-terminal domain (CTD) of the largest subunit of RNA polymerase II and functions as a scaffold for RNA processing machineries (PubMed:10907853). 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. No visible phenotype under normal growth conditions, probably due to the redundancy with PPRP40A and PPRP40C. Belongs to the PRPF40 family.