Transcription of rat-liver chromatin with homologous enzyme.

The product of transcription of rat-liver chromatin with homologous rat-liver Form-B polymerase in vitro is high molecular weight RNA with sedimentation coefficients principally in the range of 18-45 S. The average size is somewhat smaller than that of the heterogeneous high molecular weight RNA synthesized by the endogenous enzyme in vivo (or in isolated nuclei). We have excluded the possibility that this difference can be attributed to degradation of the nascent RNA occurring under the conditions of our experiments. The size of the RNA produced by the homologous enzyme nevertheless approaches that of the natural transcripts much more closely than does that of the RNA produced by bacterial RNA polymerases, which we, in addition to other authors, have found to sediment around 10 S.