NIPP-1, A NUCLEAR INHIBITORY SUBUNIT OF PROTEIN PHOSPHATASE-1, HAS RNA-BINDING PROPERTIES

NIPP-1 is a nuclear inhibitory subunit of protein phosphatase-1 with s tructural similarities to some proteins involved in RNA processing, We report here that baculovirus-expressed recombinant NIPP-1 displays RN A-binding properties, as revealed by North-Western analysis, by UV-med iated cross-linking, by RNA mobility-shift assays, and by chromatograp hy on poly(U)- Sepharose, NIPP-1 preferentially bound to U-rich sequen ces, including RNA-destabilizing AUUUA motifs. NIPP-1 also associated with single-stranded DNA, but had no affinity for double-stranded DNA. The binding of NIPP-1 to RNA was blocked by antibodies directed again st the COOH terminus of NIPP-1, but was not affected by prior phosphor ylation of NIPP-1 with protein kinase A or casein kinase-2, which decr eases the affinity of NIPP-1 for protein phosphatase-1. The catalytic sub unit of protein phosphatase-1 did not bind to poly(U)Sepharose, bu t it bound very tightly after complexation with NIPP-1. These data are in agreement with a function of NIPP-1 in targeting protein phosphata se-1 to RNA.