The mouse S‐antigen gene

Abstract

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

The arrestin superfamily: cone arrestins are a fourth family

“…3. Deduced amino acid sequences of 18 arrestin proteins aligned by CLUSTAL V. Human S-antigen (HU SAG) [13], rat S-antigen (RAT SAG) [14,5], mouse S-antigen (MUS SAG) [15], bovine S-antigen (BOV SAG) [16], humanfl-arrestinl (HU BAR1) [17], rat fl-arrestinl (RAT BAR1) [17,5], bovine fl-arrestin 1 (BOV BAR 1) [19], human fl-arrestin2 (HU BAR2) [20], rat fl-arrestin2 (RAT BAR2) [18,2], bovine fl-arrestin2 (BOV BAR2) [21], human cone arrestin (HU CAR) [1,2], Drosophila melanogaster arrestin I (D. mel I) [22,23], Drosophila melanogaster arrestin II (D. mel II) [24,25], Drosophila miranda arrestin (D. miranda) [26], Limulus arrestin (LIM) [27], Loeusta arrestin (LOCUST) [28], and Heliothis arrestin (Heliothis) [28]. Gaps (-) were introduced to obtain maximum similarity.…”

The proximal promoter of the mouse arrestin gene directs gene expression in photoreceptor cells and contains an evolutionarily conserved retinal factor-binding site.

“…As a first step toward identifying cisacting sequences that regulate arrestin expression, a search for evolutionarily conserved sequences in the 5' flanking region of arrestin genes from different mammalian species was conducted. The 5' flanking sequences of human and mouse arrestin genes have been reported previously (40,44).…”

“…Derived sequences were analyzed with the Ideas program written by Kanehisa (23). The transcriptional start site was determined by primer extension of retinal bovine arrestin mRNA by using two bovine primers (positions +64 to +89 and positions +107 to +132) and the protocols described elsewhere (40,44).…”

Immediate Upstream Sequence of Arrestin Directs Rod-specific Expression in Xenopus

“…Analysis of genomic structure showed that the structural organization at the 5Ј end of Xenopus rod arrestin is conserved with mouse and human arrestin genes (56,58). However, sequences in the immediate upstream region of the Xenopus rod arrestin gene do not exhibit significant overall homology with conserved mammalian upstream regions, in contrast to that observed for opsins (43).…”

“…4A). There is no apparent TATA motif in the upstream sequence, consistent with other arrestin genes (58,56) and with Xenopus rhodopsin (43) and transducin ␣-subunit 2 genes. However, a TATA-like sequence (ATATT) located at Ϫ25 could potentially function as a TATA-binding protein site (Fig.…”