A gizzard cDNA library was screened by the two-hybrid hybtem using as bait the S isoform of the catalytic subunit of protein phosphatase 1 (PP1δ) Among the proteins identified was a fragment of the polypyrimidine tract-binding protein-associated splicing factor (PSF) and for 242 residues was 97.1% identical to the human isoforms. Binding of PSF and PP1δ was confirmed by inhibition of phosphatase activity and by an overlay technique. The PP1δ binding site was contained in the N-terminal 82 residues of the PSF fragment. PSF may therefore act as a PPl target molecule in the spliceosome.
