MOLELCULAR BIOLOGY OF PHOTOTRANSDUCTION

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We have characterized the S-antigen genes from human and mouse, a kinase cDNA from human; phosducin cDNAs from cow, rat, and human; Shuzin cDNAs from human and cow and a Shuzin gene from human. The gene sequences of the human and mouse S-antigens were determined. The S-antigen genes were approximately 50 kbp in length, contained 16 exons and 15 introns, and were comprised of 97% intron and 3% exon. The 5'-flanking regions of the genes, approximately 1.5 kbp long, have no known regulatory elements for transcription such as TATA, GC, or CCAAT boxes. Interestingly, the 5' flanking regions of the human and mouse genes expressed tissue specific promoter activity in both in vitro and in vivo transcription assays as well as in transgenic mice. Several cDNAs of the phosducin from human, rat, and cow were isolated, and we determined their DNA sequences. Each sequence contains a Ser73 for phosphorylation by A-kinase. Sequencing results show that the phosducin in the retina and pineal gland have the same sequences and the same phosphorylation sites. This suggests that the functional role of this protein is the same in the retina and pineal gland. The functional role of the retinal protein Shuzin is unknown. We isolated several cDNAs and sequenced each of these from human and cow. The entire gene sequence of human Shuzin was also determined. This gene is composed of two introns and three exons and it has a highly repetitive sequence in the 5'-noncoding region. We have constructed fusion genes containing a 5'-flanking S-antigen gene sequence upstream of the bacterial gene chloramphenicol acetyl transferase (CAT). A hybrid gene containing the 5'-flanking region of the mouse S-antigen gene and the CAT gene was microinjected into transgenic mice. Those mice expressed CAT activity in the retina and pineal gland, suggesting that the 1300 bp-long S-antigen promoter has a tissue specific enhancer and promoter. S-antigen cDNAs were subcloned into two expression vector systems. The expressed protein was purified by gel filtration, and crystallization of this protein is now in progress.