Comparison of the active and inactive chromatin structures of genes transcribed by RNA polymerases I and II.

The coding sequences of the yeast 35S rDNA gene and of the yeast galactokinase gene both show clear staphylococcal nuclease nucleosome profiles under conditions in which the gene is inactive (galactokinase) or less active (rDNA). Under conditions of more active expression, the galactokinase gene shows marked smearing in the digestion profiles. The rDNA gene shows a qualitatively similar change in digestion patterns. There is a typical nucleosomal DNase I ladder on the coding sequences of both genes, regardless of the state of activity. In contrast to the coding sequences, the rDNA upstream region chromatin shows a nonnucleosomal profile. The nonnucleosomal character is more pronounced when the gene is more active. On the galactokinase upstream region chromatin, there is a nucleosomal structure, with some minor modifications, when the gene is inactive and a clear nonnucleosomal structure when the gene is expressed.