Research in my laboratory is directed toward understanding the processes by which glycerol 3-phosphate (glycerol-P) is used by Escherichia coli. Because we are interested in studying regulation of expression of the required genes, and in the structure, function and regulation of the proteins encoded by these genes, both biochemical and molecular genetic approaches are being used in this work.

Major emphasis has been placed on answering the question of how proteins interact at specific sites on DNA to regulate gene expression. A detailed understanding of DNA-protein interactions at the molecular level is needed in order to understand how the flow of genetic information is regulated in all organisms. The system for utilization of glycerol-P in E. coli is a good model for this purpose because of its complexity coupled, at the same time, with its amenability to biochemical-genetic analysis. The genes required for utilization of glycerol-P as carbon and energy sources are subject to four overlapping types of control, all mediated by specific DNA-protein interactions. Our work has concentrated on purification and characterization of the repressor encoded by the glpEGR operon and identification of repressor binding sites (operators) located within four different operons on the chromosome. The amino acid sequence of the repressor has been deduced from the nucleotide sequence of the glpR gene. The interaction between the repressor and its operators has been investigated by systematic alteration of the repressor and operators using oligonucleotide-directed mutagenesis. Additional work is needed to elucidate the roles of the glpE and glpG gene products.

Besides serving as a source of energy, glycerol-P is also a direct precursor for biosynthesis of the membrane phospholipids in E. coli. Work in this area is aimed at characterization of the plsX gene. The biochemical function of the plsX gene product has not been defined, but it appears to be involved in regulation of glycerol-P or fatty acid supply for phospholipid synthesis. DNA carrying the plsX gene and two neighboring genes, including fabD (fatty acid biosynthesis) and fabH has been cloned and sequenced. These genes appear to be arranged in a polycistronic operon and are probably all involved in fatty acid biosynthesis. We have found that transcription of these genes is initiated at a promoter located upstream of a gene required for ribosome synthesis. The juxtaposition of these genes may be responsible for coordination of the synthetic rates of the membrane lipids and the ribosomes. Additional work is needed to determine molecular details regarding regulation of this group of genes.

Wolfe, M. D., Ahmed, F., Lacourciere, G. M., Lauhon, C. T., Stadtman, T. C., and Larson, T. J. (2004) Functional diversity of the rhodanese homology domain. J. Biol. Chem. 279:1801-1809.   [Abstract]

Ray, W. K. and Larson, J. T. (2004) Application of AgaR repressor and dominant repressor variants for verification of a gene cluster involved in N-acetylgalactosamine metabolism in Escherichia coli K-12. Mol. Microbiol. 51(3):813-826.   [Abstract]

Movahedzadeh, F., Rison, S. C. G., Wheeler, P. R., Kendall, S. L., Larson, T. J., and Stoker, N. G. (2004) The Mycobacterium tuberculosis Rv1099c gene encodes a GlpX-like class II fructose 1,6-bisphosphatase. Microbiology 150:3499-3505.   [Abstract]

Spallarossa, A., J. L. Donahue, T. J. Larson, M. Bolognesi, D. Bordo (2001) Escherichia coli GlpE is a prototype sulfurtransferase for the single-domain rhodanese homology superfamily. Structure 9:1117-1125.   [Abstract]

Ray, W. K., Zeng, G., Potters, M. B., Mansuri, A. M., and Larson, T. J. (2000) Characterization of a 12-Kilodalton Rhodanese Encoded by glpE of Escherichia coli and its Interaction with Thioredoxin. J. Bacteriol. 182:2277-2284.   [Abstract]

Palenchar, P. M., Buck, C. J., Cheng, H., Larson, T. J., and Mueller, E. G. (2000) Evidence that Thil, An Enzyme Shared Between Thiamin and 4-Thiouridine Biosynthesis, May be a Sulfur-Transferase that Proceeds Through a Persulfide Intermediate. J. Biol. Chem. 275:8283-8286.   [Abstract]

Donahue, J. L., Bownas, J. L., Niehaus, W. G., and Larson, T. J. (2000) Purification and Characterization of glpX-Encoded Fructose-1,6-Bisphosphatase, A New Enzyme of the Glycerol 3-Phosphate Regulon of Escherichia coli. J. Bacteriol. 182:5624-5627.   [Abstract]

Yang, B. and Larson, T. J. (1998) Multiple promoters are responsible for transcription of the glpEGR operon of Escherichia coli K-12. Biochim. Biophys. Acta 1396:114-126.   [Abstract]

Yang, B., Gerhardt, S. G., and Larson, T. J. (1997) Action at a distance for glp repressor control of glpTQ transcription in Escherichia coli K-12. Mol. Microbiol. 24:511-521.   [Abstract]

Zeng, G., Ye, S., and Larson, T. J. (1996) Repressor for the sn-glycerol 3-phosphate regulon of Escherichia coli K-12. Primary structure and identification of the DNA-binding domain. J. Bacteriol. 178:7080-7089.   [Abstract]