A full-length cDNA clone encoding a novel protein containing WD-40 repeats, which were frequently involved in protein-protein interactions, was isolated and-sequenced. This clone had a predicted open reading frame (ORF) encoding 350 amino acids possessing six repeats of WD-40 motif, It was most closely homologous to TRIP-1, a phosphorylation substrate of the transforming growth factor-beta type II receptor. In the process of characterizing the function of the new gene product, we found that overexpression of the gene seemed to activate mitogen-activated protein kinase and to promote anchorage-independent growth of the cells, Moreover, the gene product was frequently overexpressed in human tumor breast tissues compared with their normal breast tissues, suggesting that the gene might be involved in the tumor progression, Radiation hybrid mapping placed the gene into human chromosome 12q11-12 near the marker D12S1593.