Regulatory sequences and nuclear factors governing tissue-restricted expression of the mouse arrestin gene were investigated. The results showed that while proximal promoter sequence positions -38 to +304 are sufficient to direct low levels of retina-specific gene expression, sequences extending upstream to position -209 support higher levels of expression in the retina, as well as detectable expression in the lens, pineal gland, and brain. Within the interval between positions -209 and -38, a broadly expressed nuclear factor, Bd, binds to sequences centered between positions -205 and -185, a region which contains two direct repeats of the hexamer, TGACCT. The proximal promoter binds three apparently retina-specific nuclear factors, Bpl, Bp2, and Bp3, through overlapping sequences centered between positions -25 and -15. Bpl and Bp3 also recognize a closely related sequence found in the promoter regions of several other vertebrate photoreceptor-specific genes. Moreover, the consensus binding site for Bpl, designated PCE I, is identical to RCS I, an element known to play a critical role in eliciting photoreceptor-specific gene expression in DrosophUia melanogaster. The results suggest that PCE I and RCS I are functionally as well as structurally similar and that, despite marked differences in the fly and vertebrate visual systems, the transcriptional machinery involved in photoreceptorspecific gene expression has been strongly evolutionarily conserved.
Phosducin, a principal protein of the retinal photoreceptor cells, modulates the phototransduction cascade by interacting with transducin. Recently, it has been reported that phosducin is a protein virtually identical to the G-protein inhibitor protein (GIP) in brain. Here, we have sequenced the complete human gene (PDC) and 2215 bp of its 5'-flanking region. The gene is 18 kb in length and has four exons and three introns. The splicing sites for donor and acceptor are in good agreement with the GT/AG rule. Comparative studies of human and mouse phosducin revealed highly homologous sequences. Both the human phosducin gene and a mutant gene locus for Usher syndrome type II have been assigned to chromosome 1q25-q32. The association of this gene with a human disease locus suggests that phosducin may be a potential candidate gene for this disorder.
We have characterized a gene for mouse S-antigen and compared its sequence with that of corresponding human and two recently published Drosophila S-antigen genes. The mouse S-antigen gene was approximately 50 kbp in length and consisted of 16 exons and 15 introns. The length of most exons was less than 100 bp and the smallest one was only 10 bp. In contrast, the length of most introns was larger than 2 kbp and the gene consisted of 97% intron and 3% exon. Both splice sites for donor and accepter were in good agreement with the GT/AG rule. S-antigen genes in human and mouse were highly conserved. In contrast, genes for the Drosophila 49-kDa arrestin homolog and arrestin consist of three introns and four exons and two introns and three exons, respectively. The 5'-flanking region of the mouse S-antigen gene, approximately 1.0 kbp long, had no regulatory elements for transcription such as the TATA, CAAT and GC boxes, while a Drosophifu arrestin gene has TATA and CAAT boxes. Interestingly, the 5'-flanking region of the mouse gene had promoter activity in an in vitro transcription assay using a nuclear extract of rat brain. A major transcription start site was found at 387 bp upstream from the translation start codon ATG in mouse. From our results, and those of others, we suggest that the S-antigen gene has evolved from a coinman ancestor gene by either insertion or deletion of introns. Such an alteration of gene structure may have played a role in the evolution of the S-antigen.Phototransduction, which converts light energy into neuronal impulse, takes place in the photoreceptor cells of the retina. Initially, light activates rhodopsin, the photoactivated rhodopsin then interacts with transducin, which in turn activates cGMP phosphodiesterase which then hydrolyzes cGMP. The decrease in intracellular concentration of cGMP modulates the influx of Na' ions through plasma-membrane channels and initiates membrane hyperpolarization [I, 21. Shortly after light activation, rhodopsin is phosphorylated by rhodopsin kinase and this modification is thought to be involved in deactivation of phototransduction [3, 41. In contrast to the mammalian system, Drosophila phototransduction differs from that of vertebrates. Phospholipase C, instead of phosphodiesterase, catalyzes the hydrolysis of phosphatidyl inositol 4,5-bisphosphate to inositol trisphosphate [5].One of the major soluble proteins in photoreceptor cells, S-antigen, has been well characterized [6]. This protein is also referred to as 48-kDa protein or arrestin [4,7, 81 and is known to have an inhibitory role in the activated phototransduction cascade [3,8]. Although the exact mechanism of the inhibition is unknown, it is postulated that S-antigen binds to photoexcited, phosphorylated rhodopsin and quenches the activation of light-dependent cGMP phosphodiesterase [3, 7, 9, Corre.~pondencc to
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.