IDENTIFICATION AND CHARACTERIZATION IN XENOPUS OF XSMGGDS, A RALB BINDING-PROTEIN

We have previously isolated a cDNA coding for a RalB protein from a Xe nopus maternal library. By mutagenesis of RalB and microinjection of i ts mRNA in embryos we show that RalB is involved in Xenopus early deve lopment. We have used the yeast two-hybrid system to screen a Xenopus maternal cDNA library in order to isolate proteins interacting to RalB . We have identified a fall-length cDNA encoding a protein homologuous to mammalian smgGDS. The Xenopus gene shows 84.6% identity with the m ammalian counterpart and contains one additional armadillo repeat. The XsmgGDS mRNA is expressed from oogenesis up to late embryogenesis at a higher level than that in adult tissues. Thus RalB is another protei n that interacts with smgGDS which suggests that RalB may be activated by a Ras independent pathway. (C) 1998 Academic Press.