The Saccharomyces cerevisiae HUT1 gene (scHUT1) and the Schizosaccharomyces pombe hut1(+) gene (sphut1(+)) encode hydrophobic proteins with approximately 30% identity to a human UDP-galactose transporter-related gene (UGTrel1) product. These proteins show a significant similarity to the nucleotide sugar transporter and are conserved in many eukaryotic species, but their physiological functions are not known. Both scHUT1 and sphut1(+) genes are non-essential for cell growth under normal conditions, and their disruptants show no defects in the modification of O- and N-linked oligosaccharides, but are sensitive to a membrane-permeable reducing agent, dithiothreitol (DTT). Consistent with this phenotype, scHUT1 has genetic interaction with ERO1, which plays an essential role in the oxidation of secretory proteins at the endoplasmic reticulum (ER). Overexpression of the MPD1 or MPD2 genes, which were isolated as multicopy suppressors of protein disulphide isomerase (PDI) depletion, could not replace the essential function of PDI in Delta hut1 S. cerevisiae cells. Our results indicate that scHut1p and spHut1p are functional homologues, and their physiological function is to maintain the optimal environment for the folding of secretory pathway proteins in the ER.
The Saccharomyces cerevisiae HUT1 gene (scHUT1) and the Schizosaccharomyces pombe hut1+ gene (sphut1 + ) encode hydrophobic proteins with approximately 30% identity to a human UDP-galactose transporter-related gene (UGTrel1) product. These proteins show a significant similarity to the nucleotide sugar transporter and are conserved in many eukaryotic species, but their physiological functions are not known. Both scHUT1 and sphut1+ genes are non-essential for cell growth under normal conditions, and their disruptants show no defects in the modification of O-and N-linked oligosaccharides, but are sensitive to a membrane-permeable reducing agent, dithiothreitol (DTT). Consistent with this phenotype, scHUT1 has genetic interaction with ERO1, which plays an essential role in the oxidation of secretory proteins at the endoplasmic reticulum (ER). Overexpression of the MPD1 or MPD2 genes, which were isolated as multicopy suppressors of protein disulphide isomerase (PDI) depletion, could not replace the essential function of PDI in Dhut1 S. cerevisiae cells. Our results indicate that scHut1p and spHut1p are functional homologues, and their physiological function is to maintain the optimal environment for the folding of secretory pathway proteins in the ER.
NAD + , an essential molecule involved in a variety of cellular processes, is synthesized through de novo and salvage pathways. NAD + synthetase catalyses the final step in both pathways. Here we show that this enzyme is encoded by the QNS1 gene in Saccharomyces cerevisiae. Expression of Escherichia coli or Bacillus subtilis NAD + synthetases was able to suppress the lethality of a qns1 deletion, while a B. subtilis NAD + synthetase mutant with lowered catalytic activity was not. Overexpression of QNS1 tagged with HA led to elevated levels of NAD + synthetase activity in yeast extracts, and this activity can be recovered by immunoprecipitation using anti-HA antibody. An allele of QNS1 was constructed that carries a point mutation predicted to reduce the catalytic activity. Overexpression of this allele, qns1 G521E , failed to elevate NAD + synthetase levels and qns1 G521E could not rescue the lethality caused by the depletion of Qns1p. These results demonstrate that NAD + synthetase activity is essential for cell viability. A GFP-tagged version of Qns1p displayed a diffuse localization in both the nucleus and the cytosol. Finally, the rat homologue of QNS1 was cloned and shown to functionally replace yeast QNS1, indicating that NAD + synthetase is functionally conserved from bacteria to yeast and mammals.
A congenital left coronary artery anomaly originating from the right aortic sinus is a rare congenital defect associated with the risk of sudden death in young individuals. In most cases, the proximal portion of the anomalous left coronary artery exists between the ascending aorta and pulmonary trunk, and it has an intramural aortic course; this could critically impair the left coronary flow owing to compression of the anomalous left main trunk between the great vessels during exercise. Herein, we report a 14-year-old boy who experienced cardiac collapse due to an acute myocardial infarction after long-distance running. After resuscitation using percutaneous cardiopulmonary support, computed tomography and coronary angiography revealed an anomalous origin of the left main coronary artery in the right sinus of Valsalva and a proximal course between the aorta and pulmonary trunk. The patient was successfully treated using an unroofing procedure of the intramural left coronary artery.
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