SITE-DIRECTED MUTAGENESIS OF THE CGMP PHOSPHODIESTERASE-GAMMA SUBUNITFROM BOVINE ROD OUTER SEGMENTS - ROLE OF SEPARATE AMINO-ACID-RESIDUESIN THE INTERACTION WITH CATALYTIC SUBUNITS AND TRANSDUCIN ALPHA-SUBUNIT

The recombinant and 21 mutant phosphodiesterase (PDE) gamma subunit (P DEgamma) genes were expressed by sequential transcription and translat ion in vitro. Inhibitory properties of these mutants and their interac tions with PDE catalytic and transducin alpha subunits were studied. T he interaction of the PDE gamma subunit with the catalytic ones procee ds in two steps - primary binding and inhibition. The central region o f the PDEgamma molecule enriched with the basic amino acid residues (p articularly, Lys-29, Lys-31 and Arg-33), is involved in the primary bi nding, and the PDEgamma C-terminus plays the key role in inhibition. T he spatial orientation of the C-terminus is of great importance here. The PDEgamma C-terminus also affects binding to catalytic moieties.