Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To examine the mechanisms responsible for tissue-specific, nutritional, and metabolic regulation of the GLUT4/muscle-adipose specific glucose transporter, we isolated and characterized the properties of the rat GLUT4 gene. Examination of the sequenced 2.5-kilobase flanking DNA revealed substantial identity with that of the mouse and human GLUT4 genes, with the greatest degree of sequence identity within the proximal 1000 basepairs up-stream of the GLUT4 open reading frame. Primer extension analysis identified a unique single transcription initiation site 176 basepairs up-stream from the start of translation. However, ribonuclease mapping revealed the presence of a previously undescribed alternatively spliced form of GLUT4 messenger RNA. Approximately 75% of the GLUT4 transcripts consisted of a fully spliced messenger RNA, and 25% was expressed as an unspliced intron-containing species. The ratios of 5' spliced and unspliced messages were invariant in adipose, cardiac, and skeletal muscle tissues. In vitro translation of reporter constructs containing both the spliced and unspliced leader demonstrated a functional difference between these two transcripts, with the unspliced form translated approximately 5-fold more than the fully spliced species. These data demonstrate the presence of 5'-heterogeneity of the GLUT4 transcripts, which underlies differences in translational efficiency in vitro.
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PMID:Characterization of 5'-heterogeneity of the rat GLUT4/muscle-adipose glucose transporter gene product. 772 Jun 44

Basal, "insulin-independent" glucose uptake into skeletal muscle is provided by glucose transporters positioned at the plasma membrane. The relative amount of the three glucose transporters expressed in muscle has not been previously quantified. Using a combination of qualitative and quantitative ribonuclease protection assay (RPA) methods, we found in normal human muscle that GLUT1, GLUT3, and GLUT4 mRNA were expressed at 90 +/- 10, 46 +/- 4, and 156 +/- 12 copies/ng RNA, respectively. Muscle was fractionated by DNase digestion and differential sedimentation into membrane fractions enriched in plasma membranes (PM) or low-density microsomes (LDM). GLUT1 and GLUT4 proteins were distributed 57% to 67% in LDM, whereas GLUT3 protein was at least 88% in the PM-enriched fractions. These data suggest that basal glucose uptake into resting human muscle could be provided in part by each of these three isoforms.
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PMID:Comparison of GLUT1, GLUT3, and GLUT4 mRNA and the subcellular distribution of their proteins in normal human muscle. 1114 24