A purification procedure for small amounts of radioactive Escherichia coli RNA polymerase

Isolation and properties of an inhibitor of Escherichia coli RNA polymerase

An inhibitor of the Escherichia coli RNA polymerase has been isolated from E. coli and has been partially characterized. The inhibitor, a polypeptide of molecular weight 70000, acts to shut off RNA synthesis at about the time that the first round of RNA synthesis is over, preventing any further RNA synthesis. The inhibitor apparently does not recognize specific termination sequences in the DNA template, since it works equally well with double-stranded DNA, single-stranded DNA and poly[d(A-T)] as templates for RNA synthesis, and because the RNA molecules synthesized from T7 DNA appear to be terminated at the same site either in the presence or absence of the inhibitor. Several experiments indirectly indicate that the inhibitor may reversibly bind to the RNA polymerase at the termination step, in a ratio of approximately one inhibitor molecule per polymerase molecule.

Rapid micromethod for the purification of Escherichia coli ribonucleic acid polymerase and the preparation of bacterial extracts active in ribonucleic acid synthesis

A rapid micromethod is described for the preparation of nucleic acid-free extracts from Escherichia coli that involves precipitation with polyethylene glycol. Extracts can be prepared from growing cells in 75 min by three short, low-speed centrifugations. The extract did not inhibit added purified ribonucleic acid (RNA) polymerase, suggesting that major inhibitors of RNA synthesis had been removed. This extract should be ideal for assessing the properties of mutant RNA polymerases. The rapid chromatography of the extracts with step elution from deoxyribonucleic acid- and diethylaminoethyl-cellulose columns resulted in high yields of substantially pure RNA polymerase. We used this technique to purify 35S-labeled RNA polymerase. This system should find application for the purification of small quantities of other bacterial RNA polymerases that share the general chromatographic properties of E. coli RNA polymerase.