BIOCHEMICAL-ANALYSIS OF THE TRANSDUCIN PHOSPHODIESTERASE INTERACTION

In vertebrate rod cells, the activated alpha-subunit of rod transducin interacts with the gamma (regulatory) subunits of phosphodiesterase t o disinhibit the catalytic subunits. A 22-amino acid long region of ro d transducin involved in phosphodiesterase activation has recently bee n identified. We have used peptides from this region of rod transducin and from several other G protein alpha-subunits to study the nature a nd specificity of the G protein alpha-effector interaction. Although p eptides derived from rod transducin, cone transducin and gustducin are similar, only the rod peptide is capable of activating rod phosphodie sterase. Using substituted peptides we have identified five residues o n one exposed face of rod transducin as important to phosphodiesterase activation. These results disagree with previous models which propose that loop regions of rod transducin interact with phosphodiesterase g amma.