Sequence of the β-subunit of the phosphatidylinositol-specific phospholipase C-directed GTP-binding protein from squid (Loligo forbesi) photoreceptors

The beta-subunit (G-beta) of the squid (Loligo forbesi) visual GTP-binding protein (G-protein), thought to be associated with a phosphatidylinositol-specific phospholipase C, has been identified and the sequence of the protein determined from its cDNA. The predicted polypeptide has a very marked sequence similarity with its mammalian counterparts (80-90% identity). Squid G-beta also has somewhat lower similarity to the yeast protein STE4 (approx. 40% identity). The role of G-beta in signal transduction is discussed in the light of its pronounced structural conservation.