ISOLATION AND ANALYSIS OF THE SOYBEAN SGA2 GENE (CDNA), ENCODING A NEW MEMBER OF THE PLANT G-PROTEIN FAMILY OF SIGNAL TRANSDUCERS

We have isolated a cDNA clone from Glycine max, named SGA2, coding for a G alpha-subunit protein. The encoded polypeptide, SG alpha 2, shows a molecular mass of 45 kDa and contains most of the conserved regions involved in guanine nucleotide binding and hydrolysis. Comparison at the nucleotide and amino acid sequence levels with the other plant Ga' s shows a high degree of conservation (>85% similarity). Phylogenetic analysis of these plant genes with the other Ga's from different speci es clearly indicate that those proteins represent a new member of the heterotrimeric G-protein family, named Gp. Tissue localization of SGA2 transcripts in root, stem and leaf organs shows that this gene is wid ely expressed throughout the plant although it is most abundant in the vascular tissues of all these organs. Furthermore, the transcript is more abundant in young tissues and organ primordia than mature tissues . The high degree of sequence conservation among the plant Get's and t he differences to other species of other kingdoms, suggest that plant G proteins may function in specialized signalling processes.