INFLUENCE OF IONIC STRENGTH AND A POLYANION ON TRANSCRIPTION IN VITRO .I. STIMULATION OF AGGREGATE RNA POLYMERASE FROM RAT LIVER NUCLEI

Studies of the aggregate RNA polymerase from rat liver nuclei with or without a stimulating effect of ammonium sulphate or polyethylene sulphonate suggest that only one type of RNA polymerase is operative in the aggregate enzyme complex. Most of the stimulating effect of high ionic strength is not due to an inhibition of degradative enzymes, as shown by incubating at 17°, a temperature at which the activity of degradative enzymes is drastically decreased. It is likely that the effect of ammonium sulphate or polyethylene sulphonate is mostly to dissociate bound histones from the DNA. Our results indicate that the RNA polymerase is bound to the DNA in the aggregate enzyme as part of an initiation or transcription complex. Kinetic data suggest that several times as many RNA polymerase molecules are engaged in RNA synthesis when polyethylene sulphonate or ammonium sulphate are present. Nearest-neighbor base frequencies indicate that at 37° and at low ionic strength or in the absence of polyethylene sulphonate, the RNA synthesized resembles that of ribosomes, whereas at 17° some RNA rich in A and U is synthesized. In the presence of ammonium sulphate or polyethylene sulphonate much more RNA rich in A and U is synthesized. These results indicate that the small amount of A-U-rich RNA which is synthesized at 37° is immediately destroyed by degradative enzymes, whereas the G-C-rich RNA is much more resistant. It is suggested that at low ionic strength or in the absence of polyethylene sulphonate, the active RNA polymerase is localized mainly in the nucleolus, while in the presence of these agents it is in the extranucleolar portion of the chromatin. © 1968.