Phosducin-Like Protein 1 (Phlp1) and Phosducin-Like Orphan Protein 1 (Phlop1)
Phosducin (Phd) is a soluble phosphoprotein, selectively binding to the beta-gamma (βγ) complex of G-proteins, playing a role in intracellular signaling processes. We have molecularly identified 3 Phd isoforms expressed in the human retina. Based on their ability or inability to interact in our assay system with Gβγ proteins, we named them Phosducin-Like Protein 1 (PhLP1) or Phosducin-Like Orphan Proteins (PhLOP1 & PhLOP2), respectively. To further study these Phd isoforms and their potential involvement in normal and abnormal visual processes through genetic alterations, we identified and characterized an 85 kb P1-PhLP human genomic clone that contains PhLPl and PhLOP1. With fluorescence in situ hybridization (FISH) to human metaphase chromosomes, this P1-PhLP genomic clone was mapped to human chromosome 1q25.3. Previous work identified a gene locus for phosducin (PDC) to 1q25-q31.1 by somatic cell hybridization and in situ hybridization. Within the P1-PhLP genomic clone, the previously characterized complete PDC gene was identified; furthermore, the 5’-flanking region and a potential promoter region of PhLOP1 was identified between Exon 2 and Exon 3 of the PDC gene. Initial transfection experiments with luciferase activity reporter PhLOP1 constructs, ranging in size from 386 to 852 basepairs (bp), suggest that no tissue specific retinal promoter activity is contained in this 5’-flanking region of the PhLOP1 when compared to the high retinal specific promoter activity observed for a 123bp construct for Interphotoreceptor Retinoid-Binding Protein (IRBP). Alternatively, a represser element is still present and preventing promoter activity in the PhLOP1 constructs. These results correspond to the low levels of mRNA of the PhLOP1 observed in the retina compared to Phd. These data suggest that both PhLP1 and PhLOP1 are created through alternative splicing of the Phd gene and that a single PDC gene at 1q25.3 is responsible for these three retinal isoforms.
KeywordsFlank Region Pineal Gland Human Retina Amino Terminal Domain Carboxy Terminal Domain
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- 18.C.M. Craft, J. Xu, V.Z. Slepak, X. Zhan-Poe, X. Zhu, B. Brown, and R.N. Lolley, 1998, PhLPs and PhLOPs in the phosducin family of Gβγ binding protein, Biochemistry, in press.Google Scholar
- 20.X. Zhu and C.M. Craft, 1998, Interaction of phosducin and phosducin isoforms with a 26S proteasomal subunit, SUG1, Molecular Vision 4:13, <http://www.molvis.org/molvis/v4/pl3>Google Scholar
- 26.N. Bobola, X. Zhu, R. Ravazzolo, and C.M. Craft, Characterization of two AT-rich sequences in a minimal IRBP promoter by transient transfections in the WERI-Rb1 retinoblastoma cell line, submitted.Google Scholar
- 27.N. Bobola, E. Hirsch, A. Albini, F. Altruda, D. Noonan, and R. Ravazzolo, 1995, A single cis-acting element in a short promoter segment of the gene encoding the Interphotoreceptor Retinoid-binding protein confers tissue-specific expression, J. Biol. Chem. 170:1289–1294.Google Scholar