The role of the histones in chromatin structure is understood, but the function of most non-histone, chromatin- associated proteins, including the intensively investigated HMG (High Mobility Group) proteins, is unclear. We have cloned the genes for several HMG-like proteins from the yeast Saccharomyces cerevisiae, thus affording us the opportunity to use a combination of genetic and biochemical approaches to determine, for the first time, the biological function for chromatin-associated HMG-like proteins. To generate conditionally lethal mutations in the HMG-like proteins, cellular HMG-like genes will be replaced with cloned HMG-like genes mutagenized in vitro. All of the mutants will be biochemically analyzed for changes in RNA, DNA and protein synthesis as well as for changes in chromatin structure. The results of these experiments will define the in vivo function of each HMG-like protein. A future direction of this research is in vitro studies of the mechanisms of HMG-like protein function using the wild type and mutant proteins. Thus, a non-denaturing purification scheme using chromatographic procedures, including immunoaffinity columns, will be developed. Finally, to begin to establish the interactions of HMG-like proteins with other chromatin proteins, extragenic suppressors of the mutants in HMG-like proteins will be isolated. The proposed experiments will increase our comprehension of the eukaryotic chromosome.
