Physical methods sensitive to DNA and protein conformation will be used to study the conformation and conformational lability of chromatin at the nucleosome, the 10 nm fiber and the 30 nm fiber levels of structure. An important experimental tool in these investigations will be flow birefringence and intrinsic viscosity. Because of the large negative optical anisotropy of DNA, this technique is particularly sensitive to details of DNA conformation and conformational changes in chromatin. This laboratory is equipped with the basic instrumental facilities required and is especially qualified on the basis of experience to employ the method in experiments of this kind. Other techniques which will be used in the project will include sedimentation, high resolution thermal melting, circular dichroism spectropolarimetry, fluorescence of labelled core histones and in certain cases, neutron scattering. Studies will be focused in two major areas. I. The effects of factors known or presumed to be associated with transcription in eukaryotic systems on the conformation and conformational transitions of the nucleosome and of polynucleosome fibers. Such factors will include acetylation of N-terminal regions of core histones and the general role of these regions in nucleosome stability, histones H2A/H2B dissociation and nonhistone proteins HMG 14 and 17 binding. II. The effects of genomic sequences on nucleosome conformation and lability. For these studies, restriction and sub-cloned fragments of the mouse Beta-globin gene will be used. This gene has been cloned in quantity in this laboratory and it contains all introns and short 5 feet and 3 feet flanking regions. Nucleosomes will be formed by reconstitution with core histones on various isolated genomic DNA fragments.
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