Phosphorylation-dependent interaction between the splicing factors SAP155 and NIPP1.
NIPP1 is a ubiquitously expressed nuclear protein that functions both as a regulator of protein Ser/Thr phosphatase-1 and as a splicing factor. The N-terminal part of NIPP1 consists of a phosphothreonine-interacting Forkhead-associated (FHA) domain. We show here that the FHA domain of NIPP1 interacts in vitro and in vivo with a TP dipeptide-rich fragment of the splicing factor SAP155/SF3b(155), a component of the U2 small nuclear ribonucleoprotein particle. The NIPP1-SAP155 interaction was entirely dependent on the phosphorylation of specific TP motifs in SAP155. Mutagenesis and competition studies revealed that various phosphorylated TP motifs competed for binding to the same site in the FHA domain. The SAP155 kinases in cell lysates were blocked by the Ca(2+) chelator EGTA and by the cyclin-dependent protein kinase inhibitor roscovitine. The phosphorylation level of SAP155 was dramatically increased during mitosis, and accordingly the activity of SAP155 kinases was augmented in mitotic lysates. We discuss how the interaction between NIPP1 and SAP155 could contribute to spliceosome (dis)assembly and the catalytic steps of splicing.
Boudrez
An
A
Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
Beullens
Monique
M
Waelkens
Etienne
E
Stalmans
Willy
W
Bollen
Mathieu
M
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins; D003001:Cloning, Molecular; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004722:Endoribonucleases; D005260:Female; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D017381:Spliceosomes / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D017413:Ribonucleoprotein, U2 Small Nuclear; C491800:SAP155 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins; C021042:protein phosphatase inhibitor-1; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D004722:Endoribonucleases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C097081:PPP1R8 protein, human