This project is concerned with the biophysical and ultrastructural properties of nucleosomes and chromosomes in various physiologic states. Current experiments explore the properties of a complex formed between nomonucleosomes (upsilon l) and nonhistone proteins (i.e., HMG 14 and 17). Two of either of these proteins bind to defined locations on the surface of the nucleosome. Proposed studies will examine the interaction of these and other nonhistones to oligo-nucleosomes and large soluble chromatin. Crystals of upsilon l and HMG-upsilon l complexes have been obtained and diffraction data will continue to be collected. Ultrastructural studies have emphasized the use of stereo-EM to explore supranucleosomal structures in 3-D. We have begun experiments to visualize higher-order nucleosome packing arrangements in sea urchin sperm, in mitotic chromosomes and in the nuclei of ciliated protozoa. Several of these biological systems will be studied in our laboratory by biochemical techniques that examine the range of chromosomal proteins. Active nucleolar genes and the Balbiani Rings of Chironomus salivary gland cells have also been examined by stereo-EM. Such studies will continue on isolated nuclei and polytene chromosomes.
