Stimulatory effect of hnRNA on template activity of isolated rat liver chromatin.

Transcription of chromatin isolated from rat liver with E. coli RNA polymerase was stimulated up to five-fold with heterogeneous nuclear RNA (hnRNA) from rat liver. The transcription product had features of DNA-primed RNA. Neither cytoplasmic poly(A)-containing RNA nor high or low molecular weight cytoplasmic poly(A)-lacking RNA from rat liver exhibited stimulation of transcription. The stimulatory effect seems to be confined to middle repetitive sequences of hnRNA. With purified DNA templates, addition of hnRNA resulted in complete inhibition of transcription. The stimulatory effect of hnRNA on chromatin transcription was also observed with endogenous RNA polymerase. This effect was dependent ionic strength and was most pronounced under conditions optimal for RNA-polymerase B activity.