ISOLATION AND EXPRESSION OF A NOVEL CHICK G-PROTEIN CDNA CODING FOR AG-ALPHA(I3) PROTEIN WITH A G-ALPHA(0), N-TERMINUS

We have cloned cDNAs coding for G-protein a subunits from a chick brai n cDNA library. Based on sequence similarity to G-protein alpha subuni ts from other eukaryotes, one clone was designated G alpha(i3). A seco nd clone, G alpha(13-o), was identical to the G alpha(i3) clone over 9 32 bases on the 3' end. The 5' end of G alpha(i3-o), however, containe d an alternative sequence in which the first 45 amino acids coded for are 100% identical to the conserved N-terminus of G alpha(o) from spec ies such as rat, mouse, human, bovine and hamster. Both clones were fo und to be expressed in all tissues studied. The unusual alpha(o)-alpha (i3)-like G-protein chimera, G alpha(13-o), was found to be expressed at significantly lower levels than G alpha(i3). In vitro transcription and translation of the G alpha(i3-o) cDNA clone gave a protein of app rox. 41 kDa which stably bound guanosine 5'-[gamma-thio]triphosphate. G alpha(i3-o), appears to be the first G-protein alpha subunit cloned which contains ends that are homologous to two different alpha subunit isoforms, G alpha(o) and G alpha(i3).