Studies on the regulation of RNA synthesis in neuronal and glial nuclei isolated from rat brain.

In searching for regulatory mechanisms involved in the cell-specific neuronal and glial transcription a cell-free transcriptional system has been developed using neuronal and glial rat brain chromatin and partially purified neuronal and glial nuclear rat brain RNA polymerases. Both free and chromatin-bound (engaged) neuronal and glial RNA polymerase fractions were separated from isolated neuronal and glial rat brain nuclei to determine their transcriptive efficiency. A double number of RNA initiation sites was measured on the neuronal when compared to the glial chromatin, independently of whether the neuronal or the glial RNA polymerase preparation was used for the determination. Structural modification of the neuronal and glial chromatin template by acetylation with acetyl-coenzyme A leads to an increase of the total number of RNA initiation sites available for exogenously added rat brain RNA polymerase. This indicates that acetylation of chromatin-bound proteins is capable to render primarily restricted gene sequences transcriptable. A positive correlation exists between the extent of acetate uptake by neuronal and glial chromatin-bound histone fractions and the extent of the increase of the number of RNA initiation sites is specifically related to histone acetylation rather than to acetylation of any other chromatin protein. Significant information in this respect could be achieved by dissociation of chromatin into its principal components and selectively reconstituting DNA with specifically acetylated histone and non-histone proteins.