The ram: a novel low molecular weight GTP-binding protein cDNA from a rat megakaryocyte library.

A novel low Mr GTP-binding protein cDNA was isolated from a rat megakaryocyte cDNA library with a synthetic oligonucleotide probe corresponding to an 8-amino acid sequence specific for c25KG, a GTP-binding protein previously isolated from human platelet cytosol fraction [(1989) J. Biol. Chem. 264, 17000-17005]. The cDNA has an open reading frame encoding a protein of 221 amino acids with a calculated Mr of 25068. The protein is designated as ram (ras-related gene from megakaryocyte) protein (ram p25). The amino acid sequence deduced from the ram cDNA contains the consensus sequences for GTP-binding and GTPase domains. ram p25 shares about 23%, 39% and 80% amino acid homology with the H-ras, smg25A and c25KG proteins, respectively. The 3.5-kb ram mRNA was detected abundantly in spleen cells.