Molecular cloning of the gene for the human placental GTP-binding protein G_p (G25K): Identification of this GTP-binding protein as the human homolog of the yeast cell-division-cycle protein CDC42

We have isolated cDNA clones from a human placental library that code for a low molecular weight GTP-binding protein originally designated G_p (also called G25K). This Identification is based on comparisons with the available peptide sequences for the purified human G_p protein and the use of two highly specific anti-peptide antibodies. The predicted amino acid sequence of the protein is very similar to those of various members of the ras superfamily of low molecular weight GTP-binding proteins, including the N-, Ki-, and Ha-ras proteins (30-35% identical), the rho proteins (≈50% identical), and the rac proteins (≈70% identical). The highest degree of sequence identity (80%) is found with the Saccharomyces cerevisiae cell-division-cycle protein CDC42. The human placental gene, which we designate CDC42Hs, complements the cdc42-1 mutation in S. cerevisiae, which suggests that this GTP-binding protein is the human homolog of the yeast protein.