Rat sarcoma (Ras) family 2 of small guanosine triphosphatases (GTPases)
The Ras2 subfamily, found exclusively in fungi, was first identified in Ustilago maydis. In U. maydis, Ras2 is regulated by Sql2, a protein that is homologous to GEFs (guanine nucleotide exchange factors) of the CDC25 family. Ras2 has been shown to induce filamentous growth, but the signaling cascade through which Ras2 and Sql2 regulate cell morphology is not known. Most Ras proteins contain a lipid modification site at the C-terminus, with a typical sequence motif CaaX, where a = an aliphatic amino acid and X = any amino acid. Lipid binding is essential for membrane attachment, a key feature of most Ras proteins.