RNA POLYMERASE II OF Escherichia coli

ABSTRACT. A second form of the DNA-dependent RNA polymerase has been isolated and partially characterized. This new form, RNA polymerase II, like RNA polymerase I, contains the α and s subunits and the σ factor. The α subunits of polymerase II are slightly smaller than those of polymerase I. Another difference is that the holo or core enzyme of polymerase II has an extra polypeptide of about 50,000 dal-tons which is absent in polymerase I. RNA polymerase II (like I) is sensitive to rifampicin, but resistant when isolated from rifampicin resistant cells. The template and metal ion cofactor requirements of the two forms of this enzyme are different. RNA polymerase II uses Mn ++ ion much better than Mg ++ ion as a cofactor, and poly dAT is by far the best template for this enzyme. Polymerase II is almost inactive in transcribing natural DNA templates. However, it apparently binds to some of those templates because it has a repressor-like in vitro effect. It inhibits the transcription of T4 DNA, but not T7 DNA, by RNA polymerase I. This might reflect an in vivo regulatory role on transcription by RNA polymerase II. It occurs in late log-stationary phase cells, but apparently not in actively growing cells.