title: Function and expression of flavohemoglobin in Saccharomyces cerevisiae. Evidence for a role in the oxidative stress response.
abstract: We have studied the function and expression of the flavohemoglobin (YHb) in the yeast Saccharomyces cerevisiae. This protein is a member of a family of flavohemoproteins, which contain both heme and flavin binding domains and which are capable of transferring electrons from NADPH to heme iron. Normally, actively respiring yeast cells have very low levels of the flavohemoglobin. However, its intracellular levels are greatly increased in cells in which the mitochondrial electron transport chain has been compromised by either mutation or inhibitors of respiration. The expression of the flavohemoglobin gene, YHB1, of S. cerevisiae is sensitive to oxygen. Expression is optimal in hyperoxic conditions or in air and is reduced under hypoxic and anaerobic conditions. The expression of YHB1 in aerobic cells is enhanced in the presence of antimycin A, in thiol oxidants, or in strains that lack superoxide dismutase. All three conditions lead to the accumulation of reactive oxygen species and promote oxidative stress. To study the function of flavohemoglobin in vivo, we created a null mutation in the chromosomal copy of YHB1. The deletion of the flavohemoglobin gene in these cells does not affect growth in either rhoo or rho+ genetic backgrounds. In addition, a rho+ strain carrying a yhb1(-) deletion has normal levels of both cyanide-sensitive and cyanide-insensitive respiration, indicating that the flavohemoglobin does not function as a terminal oxidase and is not required for the function or expression of the alternative oxidase system in S. cerevisiae. Cells that carry a yhb1(-)deletion are sensitive to conditions that promote oxidative stress. This finding is consistent with the observation that conditions that promote oxidative stress also enhance expression of YHB1. Together, these findings suggest that YHb plays a role in the oxidative stress response in yeast.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA.
authors.forename: X J
authors.initials: XJ
authors.lastname: Zhao
authors.forename: D
authors.initials: D
authors.lastname: Raitt
authors.forename: P
authors.initials: P
authors.lastname: V Burke
authors.forename: A S
authors.initials: AS
authors.lastname: Clewell
authors.forename: K E
authors.initials: KE
authors.lastname: Kwast
authors.forename: R O
authors.initials: RO
authors.lastname: Poyton
mesh_terms: D003958:Diamide / Q000494:pharmacology; D049308:Dioxygenases; D004352:Drug Resistance, Microbial; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005800:Genes, Fungal; D006420:Hemeproteins / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D008298:Maleates / Q000494:pharmacology; D018384:Oxidative Stress; D010100:Oxygen / Q000494:pharmacology; D010269:Paraquat / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D013045:Species Specificity; D013053:Spectrophotometry; D014158:Transcription, Genetic
chemical_list: D006420:Hemeproteins; D008298:Maleates; D029701:Saccharomyces cerevisiae Proteins; D003958:Diamide; D006861:Hydrogen Peroxide; D049308:Dioxygenases; C101796:YHB1 protein, S cerevisiae; C014476:diethyl maleate; D010269:Paraquat; D010100:Oxygen