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Purification and characterization of coliphage N4 RNA polymerase II activity from infected cell extracts.

The soluble components of the RNA polymerase activity (N4 RNA polymerase II) required for coliphage N4 middle RNA synthesis have been purified to homogeneity using a complementation assay described elsewhere. These soluble components are found to exhibit the properties of a DNA-dependent RNA polymerase which is resistant to both rifampicin and streptolydigin and transcribes denatured N4 DNA with marked preference but with little selectivity for the middle region of the N4 genome. In its native form, the activity is composed of one Mr = 40,000 polypeptide (p4, the product of N4 cistron 4) and one Mr = 30,000 polypeptide (p7, the product of N4 cistron 3). Its physical properties and the mechanism of transcription selectivity are discussed.