Molecular cloning of a member of a new class of low-molecular-weight GTP-binding proteins.

We report the cloning of a low-molecular-weight GTP-binding protein that appears to be the first member of a new class of G proteins. This G protein was cloned from the HT4 neural cell line and has the closest homology to the rab, sec4, and ypt1 members of the low-molecular-weight (LMW) G-protein family. The amino acid sequence identity is only 30% with these other LMW G proteins, but in the four conserved GTP-binding domains, amino acid identity increases to 50-100%. A unique feature that distinguishes this G protein from other LMW G proteins is its carboxy-terminal amino acid sequence -Cys-Cys-Pro. In keeping with the current nomenclature for other members of the ras superfamily, we will designate this new class as rah (ras-related homolog). On the basis of sequence homology, rah may function in vesicular trafficking and possibly in neurotransmitter secretion.