The chromatin structure of an actively expressed, single copy yeast gene.

When the yeast galactokinase gene is not active (repressed, not expressed, quiescent), there is an exceptionally regular nucleosome array on coding sequence galactokinase chromatin, as shown by both denaturing and non-denaturing gel analysis of staphylococcal nuclease digests. Expression of the gene results in a limited smearing of the nucleosome repeat peaks and an increase in interpeak DNA, appearing as a regular ladder of DNA bands on denaturing gels. On non-denaturing gels the pattern is more complex and molecular weight dependent. These data suggest an increase in intracore particle DNA accessibility, allowing staphylococcal nuclease to digest throughout the nucleosome in expressed chromatin. Comparison to bulk chromatin and to an operationally inactive gene (35S rDNA) show that the alteration is specific to expressed chromatin. In contrast, DNase I shows no differences in the digestion of the gene specific chromatin in expressed or inactive states.