IDENTIFICATION OF A NOVEL DROSOPHILA SMAD ON THE X-CHROMOSOME

TGF-beta signaling from the cell surface to the nucleus is mediated by the SMAD family of proteins, which have been grouped into three class es based upon sequence identity and function. Receptor-regulated, or p athway-restricted, SMADs (R-SMADs) are phosphorylated by ligand-specif ic serine/threonine kinase receptors, Phosphorylated R-SMADs oligomeri ze with the coactivating, or shared, SMAD (Co-SMAD) mediator and trans locate to the nucleus where the complex directs transcription of downs tream target genes. Inhibitory SMADs (I- SIMADs) block receptor-mediat ed phosphorylation of R-SMADs, In Drosophila, one member of each class of SMAD has been reported: MAD, an R-SMAD MEDEA, a Co-SMAD, and DAD, an I-SMAD, Here, we report the first identification of a novel Drosoph ila R-SMAD, which we have named Smox for Smad on X We have localized t he Smox gene to a specific interval on the X chromosome and shown that Smox is transcribed throughout development, (C) 1998 Academic Press.