Assistant Professor - Department of Biochemistry and Cell Biology
Major research interests: The regulation of membrane composition and the role of membrane composition in determining cellular properties; source-sink interactions in plants.
Membrane composition: Membrane composition is postulated to affect many cellular properties, such as tolerance to extreme temperatures and organellar and sub-organellar morphology. The reg-ulation of membrane composition is a particularly mysterious process since lipids are insoluble molecules, raising the question of how lipid biosynthetic proteins contained within one cellular compartment can be sensitive to the lipid composition of membranes in other cellular compartments.
Genes encoding four of the fatty acid desaturases that are involved in regulating membrane composition have been isolated from the plant Arabidopsis thaliana. These genes are being used as tools to elucidate the mechanism by which the complex regulation of membrane composition is accomplished. Transgenic plants that have increased levels of desaturase activity, as well as mutants of Arabidopsis thaliana that are deficient in desaturase activity, are being used to determine the effect of altering membrane composition on such cellular properties as cold and heat tolerance and organellar morphology.
Source-sink interactions in plants: Sources of fixed carbon (i.e., mature leaves) are thought to interact with sinks for fixed carbon (immature leaves, stems, roots, seeds, etc.) in complex and poorly understood ways that play an important role in plant development and physiology as well as in determining crop yields.
The ways in which source-sink interactions are controlled are not known but are likely to involve the regulations of critical genes by either soluble sugar levels or by the level of some compound that varies in proportion to soluble sugar concentrations. For this reason, genes that are regulated by sugar concentrations, as well as mutants of the plant Arabidopsis thaliana that are deficient in this regulation, are being identified.
Assistant Professor - Department of Biochemistry and Cell Biology
The primary goal of research in our laboratory is directed towards obtaining a better understanding of the structure-function relationships underlying biologically relevant nucleic acid systems. To this end, the three-dimensional structure and dynamics of RNA and RNA-associated systems are studied using heteronuclear (1H-[13C, 15N, 31P]) NMR spectroscopy and a variety of computational methods. The data obtained from these methods will complement biological and biochemical information when resolving RNA structure-function questions.
The discovery that RNAs can catalyze biological reactions has greatly changed our view of RNA function and has led to a renewed interest in the cellular roles of RNA. Although high resolution NMR spectroscopy and X-ray crystallography have provided detailed structures for hundreds of proteins, the structural data base for RNAs has remained small. Recent advances in RNA preparative methods now make it possible to apply modern NMR spectroscopic techniques to probe the structure of functional RNAs and RNA-ligand complexes
In modern cells, many RNAs complex with proteins to form a functional unit of the cellular machinery. Although the RNA-protein recognition is often highly specific, the particular features that give rise to a unique interaction are not well understood, but almost certainly include tertiary structure in addition to sequence and secondary structure.
Several systems are currently being investigated in our lab. One of these is an RNA-protein interaction found in the E. coli phage R17. Expression of the replicase gene of phage R17 is regulated in part by the formation of a hairpin loop structural element encompassing the translation start site of this gene. This element also acts as the nucleation site for phage capsid formation by binding tightly and specifically to the phage coat protein. We are applying 15N and 13C heteronuclear NMR methods to explore the structure and dynamics of the RNA and RNA-protein complex.
Extra-helical base insertions in duplex regions of RNA occur frequently in rRNA. The functional significance of these structural elements is unclear at this time, however, many such insertions have been found to be evolutionarily conserved. Two- and three-base bulges also occur as structural elements in other RNA systems including the TAR element of HIV. The extra-helical bases provide a convenient system with which to develop and optimize NMR spectroscopic and computational methods for nucleic acid applications. Isotopic enrichment of these systems with 13C also allows us to begin examining the dynamic or motional properties exhibited by these molecules in various contexts.
Another RNA structural motif, proposed to form an unusual hairpin loop, is found in the 5' noncoding regino of the polio virus genome. Biochemical data indicate this element and others in the noncoding region are critical for the process of internal translational initiation. This RNA element has been shown to interact specifically with a host cell protein, and RNA residues critical for this interaction have been identified. Combining the biochemical data with the structural information for this molecule should provide further insights into structural features important for RNA-protein recognition.