A family of ras-like GTP-binding proteins expressed in electromotor neurons.

The cDNAs encoding seven low molecular weight (LMW) GTP-binding proteins were isolated from an electrode lobe library of the marine ray Discopyge ommata. Four were assigned as the ray homologues of previously identified LMW GTP-binding proteins rab1, ral, Krev, and rho. Three others showed unique sequences, including two exhibiting significant similarity to the yeast SEC4 protein. Northern analysis indicated that several of the transcripts are enriched in neural tissues with a moderate level of expression in cardiac muscle. This tissue distribution was corroborated with affinity purified antibodies against the LMW GTP-binding proteins. Subcellular fractionation revealed that the proteins co-purify with cholinergic synaptic vesicles. Immunohistochemical analysis confirms this localization. At least two of the proteins, oral and o-rho, are localized to the pre-synaptic terminals.