Photo of Bob Poyton

Bob Poyton

Professor
303.492.3823
Robert.Poyton@Colorado.EDU
Porter room B213B
Visit the Poyton website.

Education

Ph.D., University of California, Berkeley, 1971

B.A. Brown University, 1966

Biography

Research Interests:
Oxygen sensing and control of gene expression; mitochondrial biogenesis in the yeast Saccharomyces cerevisiae; oxidative stress and aging.

Research Profile:
Our studies address (1) gene expression, (2) targeting and assembly of membrane proteins, (3) cellular energy production, and (4) oxidative stress. We use baker's yeast, Saccharomyces cerevisiae, and employ genetics, genetic engineering with cloned genes, protein biochemistry, and in vitro gene expression systems. Our model for these studies is cytochrome c oxidase, a multi-meric protein of the inner mitochondrial membrane that is composed of three subunit polypeptides encoded by mitochondrial genes (COX1-3) and six subunits encoded by nuclear genes (COX4-9).

Gene Expression
Two aspects of gene expression are under study. First, we are examining how O2 activates transcription of COX5a and COX6 and represses transcription of COX5b. Our current goals are to identify the intracellular O2 sensor that translates O2 concentration into an effect on transcription and understand how the "O2 switch" works, locate O2 responsive promoter elements, identify proteins that bind to these O2 responsive elements, and determine how the O2 sensing pathway affects transcription. Second, we are studying how gene expression in the nucleus is coordinated with gene expression in the mitochondrion. Current studies are focused on how the mitochondrial genome regulates the expression of the nuclear COX genes. Recently, we have discovered that a mitochondrial gene is required for phosphorylation of a transcription factor that regulates the nuclear COX genes. We are now attempting to elucidate the signal transduction pathway from the mitochondrion to the nucleus.

Protein Assembly
The formation of cytochrome oxidase requires the import of nuclear-coded subunits from the cytosol, the export of mitochondrially coded subunits from the matrix, and an assembly pathway that brings both sets of subunits together. We are using newly developed in vivo and in vitro systems and "assembly defective" mutants to examine the sequence in which subunits come together during assembly and identify a new type of molecular chaperone that is involved in cytochrome c oxidase assembly.

Energy
Recently we have developed methods for studying the electron transfer reactions of cytochrome oxidase in whole cells. Now we plan to use site-directed mutagenesis to study the structural features of its nuclear-coded subunits that are important for function in vivo. In addition, we have developed a heterologous complementation system with yeast for assaying human cytochrome c oxidase subunit function and have used it to clone human cytochrome c oxidase subunits and cytochrome c oxidase specific molecular chaperones. Eventually, we hope to use this system for assaying subunit dysfunction in a growing number of human diseases (myopathies and neuropathies) that have been linked to defects in cytochrome c oxidase.

Selected Publications

Castello, P. R., David, P.S., McClure, T., Crook, Z., and Poyton, R.O. 2006.
Mitochondrial cytochrome c oxidase produces nitric oxide under hypoxic conditions: implications for oxygen sensing and hypoxic signaling in eukaryotes.
Cell Metabolism 3: 277-287.

Castello, P.R., Ball, K, Woo, D K., Wojcik, J., Liu, L. and Poyton, R. O. 2008.
Oxygen-regulated isoforms of cytochrome c oxidase have differential effects on its nitric oxide production and on hypoxic signaling.
Proc. Natl. Acad. Sci. USA. 105: 8203-8208.

Woo, D-K., T.L. Phang, J.D. Trawick, and R.O Poyton. 2009.
Multiple pathways of mitochondrial-nuclear communication in yeast: Intergenomic signaling involves ABF1 and affects a different set of genes than retrograde regulation.
BBA Genetic Regulatory Mechanisms. 1789, 135-145

Woo, D-K. and R.O. Poyton. 2009.
The absence of a mitochondrial genome in rho0 cells extends life span independently of retrograde regulation.
Exptl Gerontology. 44, 390-397.

Poyton, R. O., P.R. Castello, and K.A. Ball. 2009.
Mitochondrial Generation of Free Radicals and Hypoxic Signaling.
Trends in Endocrinology and Metabolism. 20, 332-340.

Ball KA, Castello PR, Poyton RO. 2011.
Low intensity light stimulates nitrite-dependent nitric oxide synthesis but not oxygen consumption by cytochrome c oxidase. Implications for phototherapy.
J. Photochem Photobiol. B. Biol. 102, 182-191.

Poyton, R.O. and K.A. Ball. 2011.
Therapeutic Photobiomodulation: nitric oxide and a novel role for cytochrome c oxidase.
Discovery Medicine 11, 1554-159.

Li, B., C. Skinner, P.R. Castello, M. Kato, E. Easlon, L Xie, T. Li, s-P Lu, C. Wang, T. Tsang, R.O. Poyton, and S-J. Lin. 2011.
Identification of potential calorie restriction-mimicking yeast mutants with increased mitochondrial respiratory chain and nitric oxide levels.
J. Ageing Res. 2011, Article ID 673185

Ball, K.A., A.W. Nelson, D.G. Foster, and R.O. Poyton. 2012.
Nitric oxide produced by cytochrome c oxidase helps stabilize HIF-1a in hypoxic mammalian cells.
Biochem Biophys. Res Comm. 420: 727-732

Woo, D-K., Y.W. Jung, K.M. O'Brien, and R.O. Poyton. 2013.
Molecular characterization of a mitochondrial mutant carrying a point mutation in the 3 untranslated region of the COX3 mRNA from Saccharomyces cereviae.
Animal Cells and Systems. 17: 80-87.