The purpose of this research is to find out what conformational changes are possible in chromatin. We have shown that tyrosine fluorescence is a very sensitive means for following the conformational changes of nucleosome core particles and plan to extend these studies to more complex systems. First, we will fractionate nucleosomes according to their solubilities and examine the physical properties of the different fractions to find out if different kinds of nucleosomes behave in different ways. We will use tyrosine fluorescence to study the properties and conformational transitions of complexes between core particles and HMG proteins 14 and 17. We will use tryptophan fluorescence to study the binding of HMG proteins 1 and 2 to chromatosomes and oligomers. We will also examine the conformational transitions of acetylated nucleosomes. We want to find out how chromatin structure can be modulated by modifications and the binding of chromosomal proteins. Although most of our studies will use the intrinsic fluorescence of the chromosomal proteins, we will also extrinsic fluorescence probes. In addition we will use other biophysical techniques such as circular dichrosim and ultracentrifugation where they are appropriate. Fluorescence studies will include both steady-state and lifetime measurements. We will continue our work on the development of the method of moments and F/F deconvolution approaches to the analysis of fluorescence decay data.
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