title: Quantification of protein copy number in yeast: the NAD+ metabolome.
abstract: Saccharomyces cerevisiae is calorie-restricted by lowering glucose from 2% to 0.5%. Under low glucose conditions, replicative lifespan is extended in a manner that depends on the NAD+-dependent protein lysine deacetylase Sir2 and NAD+ salvage enzymes. Because NAD+ is required for glucose utilization and Sir2 function, it was postulated that glucose levels alter the levels of NAD+ metabolites that tune Sir2 function. Though NAD+ precursor vitamins, which increase the levels of all NAD+ metabolites, can extend yeast replicative lifespan, glucose restriction does not significantly change the levels or ratios of intracellular NAD+ metabolites. To test whether glucose restriction affects protein copy numbers, we developed a technology that combines the measurement of Urh1 specific activity and quantification of relative expression between Urh1 and any other protein. The technology was applied to obtain the protein copy numbers of enzymes involved in NAD+ metabolism in rich and synthetic yeast media. Our data indicated that Sir2 and Pnc1, two enzymes that sequentially convert NAD+ to nicotinamide and then to nicotinic acid, are up-regulated by glucose restriction in rich media, and that Pnc1 alone is up-regulated in synthetic media while levels of all other enzymes are unchanged. These data suggest that production or export of nicotinic acid might be a connection between NAD+ and calorie restriction-mediated lifespan extension in yeast.
authors.affiliation: Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Szu-Chieh
authors.initials: SC
authors.lastname: Mei
authors.affiliation: Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Charles
authors.initials: C
authors.lastname: Brenner
mesh_terms: D055442:Metabolome; D009243:NAD / Q000378:metabolism*; D009525:Niacin / Q000378:metabolism; D009536:Niacinamide / Q000378:metabolism; D009535:Nicotinamidase / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000378:metabolism; D056565:Sirtuin 2 / Q000378:metabolism
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D009243:NAD; D009536:Niacinamide; D009525:Niacin; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D009535:Nicotinamidase; C474330:PNC1 protein, S cerevisiae