The primary structure of the gamma-subunit of cyclic GMP phosphodiesterase was determined by parallel analysis of the amino acid sequence of the protein and nucleotide sequence of the corresponding cDNA. The enzyme gamma-subunit contains 87 amino acid residues, its N-terminal amino group being acetylated.

The ct-subunit primary structure of cyclic GMP phosphodiesterase has been determined by parallel analysis of the protein amino acid sequence and the corresponding cDNA nucleotide sequence. The enzyme ~t-subunit contains 858 amino acid residues, its N-terminal amino group being acetylated. The partial primary structure of the enzyme fl-subunit has also been elucidated. A significant homology has been found between the ct-and fl-subunits of cGMP phosphodiesterase.

cDNA clones encoding the @bunit of the photoreceptor cGMP phosphodiesterase (PDE) were isolated from a human retina library and their sequence was determined. The encoded polypeptide consists of 854 amino acid residues with a calculated molecular mass of 98,416 Da. Alignment of the deduced amino acid sequence with the earlier analysed a-, p-and a'-subunits of bovine and mouse PDEs demonstrates a high homology. Two overlapping recombinant 1 phage clones containing 26 kb of the human PDE/%ubunit gene were isolated from the genomic library. A total nucleotide sequence of exons 4-22 of the PDE /?-subunit gene was established which completely corresponded to the cDNA structure. According to sequence analysis no potential possibility for alternative splicing of the p-subunit gene was observed between exons 20 and 21 which led to the formation of the /3'-subunit as described for mouse PDE. Polymerase chain reaction (PCR) experiments also confirm the absence of the PDE /3'-subunit in human retina.

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