Effects of cations on DNA-dependent RNA polymerase

DNA-dependent synthesis of RNA by Escherichia coli RNA polymerase: release and reinitiation of RNA chains from DNA templates

RNA synthesis in an in vitro RNA polymerase system at low ionic strength soon ceases, due to inhibition by accumulated RNA. Measurement of RNA chain initiation by the incorporation of gamma-(32)P-ATP and GTP with native T2 or T4 DNA as template shows that only one RNA chain is formed per molecule of enzyme added. In contrast, when the polymerase reaction is carried out in 10 mM Mg(++) and 0.2 M KCl, RNA synthesis proceeds nearly linearly for hours, resulting in a marked increase in accumulated RNA. Incorporation of gamma-(32)P-ATP also proceeds throughout the course of the reaction and the number of chains initiated per molecule of enzyme is increased severalfold. Most RNA chains formed are released from the DNA template as free RNA. Polymerase is released also in this process and acting catalytically reinitiates new chains. Rifampicin inhibits initiation of RNA synthesis and also blocks reinitiation of RNA chains without affecting growth of RNA chains already initiated.

Transient activation of RNA polymerase in Escherichia coli B after infection with bacteriophage T4

Sköld and Buchanan(1) have reported that there is a rapid loss of RNA polymerase activity in Escherichia coli B after infection with T4 bacteriophage. More recent studies on the mechanism of this inactivation have been made in this(2) and other laboratories.(3, 4) In this communication, we report the observation of a transient stimulation of RNA polymerase activity when measurement is made immediately after infection and when cells are ruptured by a gentle lysis procedure. The increase in activity is independent of the synthesis of protein. The activity in the extracts of infected cells is lost by treatment of the extract with antibody to E. coli RNA polymerase and is refractive to the inhibitory action of the antibiotic rifamycin. Hybridization experiments indicate that an RNA transcribed almost exclusively from a T4 DNA template is the product of incubation of extracts of infected cells with a reaction mixture containing an exogenous primer (salmon sperm DNA). These findings are consistent with the hypothesis that one of the first steps in phage infection is the formation of a transcription complex containing T4 DNA and E. coli RNA polymerase.

A factor that stimulates RNA synthesis by purified RNA polymerase

A protein factor, partially purified from E. coli, can stimulate some 30- to 50-fold the transcription of DNA by purified RNA polymerase. Evidence is presented suggesting that this stimulatory factor (designated M factor) exerts its effect before the RNA synthesis is initiated. The M factor is prepared from a crude ribosome fraction, but it does not require the presence of ribosomes for full activity.

In vitro synthesis of poliovirus ribonucleic acid: role of the replicative intermediate

Poliovirus ribonucleic acid (RNA) polymerase crude extracts could be stored frozen in liquid nitrogen without loss of activity or specificity. The major in vitro product of these extracts was viral single-stranded RNA. However, after short periods of incubation with radioactive nucleoside triphosphates, most of the incorporated label was found in replicative intermediate. When excess unlabeled nucleoside triphosphate was added, the label was displaced from the replicative intermediate and accumulated as viral RNA. It is concluded from this experiment that the replicative intermediate is the precursor to viral RNA. In addition, some of the label was chased into double-stranded RNA. The implications of this finding are discussed.

Nuclear fraction of Bacillus subtilis as a template for ribonucleic acid synthesis

A "nuclear fraction" prepared from Bacillus subtilis was a more efficient template than purified deoxyribonucleic acid for the synthesis of ribonucleic acid by exogenously added ribonucleic acid polymerase isolated from B. subtilis. The initial rate of synthesis with the nuclear fraction was higher and synthesis continued for several hours, yielding an amount of ribonucleic acid greater than the amount of deoxyribonucleic acid used as the template. The product was heterogenous in size, with a large portion exceeding 23S. When purified deoxyribonucleic acid was the template, a more limited synthesis was observed with a predominantly 7S product. However, the ribonucleic acids produced in vitro from these templates were very similar to each other and to in vivo synthesized ribonucleic acid as determined by the competition of ribonucleic acid from whole cells in the annealing of in vitro synthesized ribonucleic acids to deoxyribonucleic acid. Treatment of the nuclear fraction with heat (60 C for 15 min) or trypsin reduced the capacity of the nuclear fraction to synthesize ribonucleic acid to the level observed with purified deoxyribonucleic acid.