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V.P. Theendakara, S.R. Kar, C.K. Yamashita, N. Akhmedov, D.B. Farber; Proteins Interacting With the 3'UTR of Human ß–PDE mRNA . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4886.
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Protein content in the cell is controlled at several levels: transcriptional, post–transcriptional, and via selective protein degradation in the proteosome. Regulation at the mRNA level is faster and more economical than other regulatory mechanisms. It relies on three factors – transcript stability, localization and translation initiation. It is the 3'UTR, in most cases, which dictates the fate of a particular mRNA, by regulating transcript cleavage and polyadenylation, nuclear export, transcript stability, level of translation and mRNA targeting. Our purpose is to study the post–transcriptional regulation of the ß–PDE gene.
The 3'UTR of the human rod ß–PDE mRNA is 451nt long. Unlike the mouse or bovine ß–PDE 3'UTR, the human 3'UTR has an Alu sequence in the middle preceded by a poly–T stretch, typically associated with the Alu insertion. Significantly, there are two short sequences, one at the 5' end and the other at the 3' end of the Alu sequence that are highly conserved across species. Two 100nt RNA stretches of the UTR, each containing one of the conserved sequences in the middle, were used to identify putative retinal trans–acting factors.
Electrophoretic mobility shift assays and UV–cross linking studies of these two RNA fragments in the presence of extracts of Y79 retinoblastoma cells yielded several putative binding factors. Mass spectroscopic analysis identified several candidates binding to the RNA fragments. Based on our results, we chose to study one of the putative binding factors, Hsp90, in the post–transcriptional regulation of ß–PDE. Geldanamycin (GA), a benzoquinone ansamycin, is a known inhibitor of Hsp90. A dose–dependent decrease in ß–PDE expression was observed upon addition of GA in in vitro translation assays using rabbit reticulocyte that is known to have Hsp90.
Our preliminary results indicate that Hsp90 may protect the ß–PDE transcript from degradation and thereby be involved in the regulation of ß–PDE translation.
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