Affiliations

Professor, Biological Chemistry

Member, Gene Regulation GPB Home Area, Immunity, Microbes & Molecular Pathogenesis GPB Home Area, JCCC Gene Regulation Program Area, Molecular Biology Institute

(1) One of the ways Salmonella, a major cause of gastroenteritis or food poisoning, evades the immune system is to change flagellar proteins, which are major cell surface antigens. Inversion of a 1 kb segment of the chromosome by the Hin recombinase regulates flagellar synthesis by switching the orientation of a transcriptional promoter. Our work has shown that Hin dimers bound to specific DNA sites flanking the inverting segment, together with regulatory proteins called Fis bound to an enhancer-like DNA segment, assemble into an ?invertasome? complex with the help of the DNA bending protein HU. DNA cutting, translocation of DNA strands, and ligation all occur within this nucleoprotein machine. We are trying to determine the molecular structure of the invertasome and the conformational changes that accompany the different reaction steps. The lab uses a variety of approaches including genetics, site-directed crosslinking, fluorescence resonance energy transfer, electron microscopy, X-ray crystallography, and molecular modeling to probe these steps. (2) Fis is one of the most abundant DNA binding proteins in rapidly growing cells, though its levels vary enormously with growth conditions. We are also studying its role as a regulator of transcription and chromosome structure. Fis selectively activates and silences transcription of specific genes, and we hope to learn how Fis couples cell physiology to global gene expression patterns. Mechanistic aspects of transcriptional activation by Fis are being defined using genetic and biochemical methods, and x-ray crystallography. We are pursuing recent data suggesting Fis performs an active role in packaging the chromosome into the nucleoid. (3) HMGB proteins are abundant constituents of eukaryotic chromatin. They deform DNA structure and collaborate with other transcription factors to co-regulate expression of a subset of genes. Our previous work has emphasized the structural and functional DNA binding properties of mammalian HMGB1 and yeast Nhp6A/B. We are using yeast as a model system to further study the various roles of HMGB proteins in modulating chromatin structure and function. Current work is focused on identifying yeast genes whose expression is co-regulated by Nhp6A/B and investigating how Nhp6A/B influence their transcription.