Characterisation of RNA Synthesis in vitro in Neurone‐Rich, Oligodendroglial and Liver Nuclei

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Abstract
In neurone‐rich nuclei isolated from the adult guinea‐pig cerebral cortex, DNA‐dependent RNA polymerase B reaction is several times more active than in liver nuclei. This may be attributable to the unusual wealth of euchromatin in mature neuronal nuclei. Nuclear RNA labelled in vitro was hydrolysed by alkali, and the number as well as the average length of nascent RNA chains were determined by measuring [3H]uridine and [3H]UMP/[3H]uridine ratio, respectively. In neurone‐rich nuclei, the number of growing RNA chains is greater, and the average chain length longer than in liver nuclie. In oligodendroglial nuclei which exhibit RNA polymerase B reaction of intermediate activity, the number of growing RNA chains is found comparable to, but the average chain length longer, than that in liver nuclei. Thus, the presence of a greater number of growing RNA chains appears to be a unique feature of neuronal nuclei. In neuronal chromatin, mean residue ellipticity in circular dichroism spectrum in the wavelength range of 260–300 nm is significantly higher than in liver and oligodendroglial chromatins, and this is in apparent correlation with the number, rather than the average length, of growing RNA chains. Digestion of chromatin with trypsin leads to reversion of the circular dichroism spectrum toward that of free DNA, and completely abolishes the difference in ellipticity pattern that is observed among native neurone‐rich, oligodendroglial and liver chromatins. In liver nuclei, RNA polymerase B reaction is greatly enhanced with trypsin, which is primarily attributable to the facilitated elongation of RNA chains that is otherwise restricted. In neuronal nuclei where the steric restriction imposed on RNA synthesis is though to be intrinsically weakened, digestion with trypsin is more than necessary in disclosing the RNA polymerase B activity. RNA synthesis in neuronal and oligodendroglial nuclei in vitro is discussed in correlation with that reported in vivo.