MOLECULAR-CLONING OF G-PROTEINS AND PHOSPHODIESTERASES FROM RAT TASTECELLS

To identify and characterize those proteins involved in taste transduc tion, we cloned G proteins and phosphodiesterases from rat taste tissu e. Using degenerate primers corresponding to conserved regions of G pr otein alpha subunits, the polymerase chain reaction was used to amplif y and clone eight distinct cDNAs: alpha(i-2), alpha(i-3), alpha(12), a lpha(14), a(s), alpha t-rod, alpha-t-cone and alpha gustducin. alpha(i -3), alpha(14), alpha(s), and alpha(t-rod) are more highly expressed i n taste tissue than in the surrounding nonsensory tissue. a gustducin is only expressed in taste cells. Rod transducin had previously been f ound only in the rod cells of the retina, where it converts light stim ulation of rhodopsin into activation of cGMP phosphodiesterase. The pr imary sequence of a gustducin shows striking similarities to rod trans ducin in the receptor interaction domain and the phosphodiesterase act ivation site. We propose that gustducin and transducin regulate phosph odiesterase activity in taste cells and that this may promote bitter t ransduction and inhibit sweet transduction. Consistent with this propo sal, we cloned two types of cAMP PDE from taste tissue: dnc-1 and PDE- 3.