EVOLUTIONARY ANALYSIS OF G-PROTEINS IN EARLY METAZOANS - CLONING OF ALPHA-SUBUNITS AND BETA-SUBUNITS FROM THE SPONGE GEODIA-CYDONIUM

G-protein-coupled (seven-transmembrane segment)-receptors represent a major group of metazoan receptors, involved in transduction of extrace llular signals. The G-proteins, which are made up of G alpha/beta/gamm a-subunits, link the receptors to the effector system(s). To analyze t he phylogenetic relationships among the metazoan alpha-subunits of G-p roteins, cDNAs of alpha-subunits were isolated from Geodia cydonium, a marine sponge belonging to the lowest metazoan phylum, Porifera. One encodes a putative isotype of a stimulator of the adenylyl cyclase (G alpha s), another one a putative inhibitor of the adenylyl cyclase (G( alpha i/o)) and the third one a putative activator of phospholipase C (G(alpha q)). In addition one putative P-subunit was a cloned from the same species. The deduced amino acid sequences of the sponge G(alpha s)-(putative M-r 44749), the G(alpha i/o)-(M-r 41064) and the G(alpha q) subunits (M-r 41363) were found to display high similarity with the corresponding sequences from higher Metazoa, and are only distantly r elated to those of slime mold, yeast or plants. Of lower similarity ar e the sequences of the beta-subunits among animals and plants, thus no t allowing robust grouping. These data demonstrate that the phylogenet ic relationships, obtained from analyses of the alpha subunits from me tazoan G-proteins, support the conclusion that all metazoan phyla, inc luding the Porifera are of monophyletic origin. (C) 1998 Elsevier Scie nce B.V.