RNA polymerase-DNA complexes I. The study of the conformation of nucleic acids at the growing point of RNA in an RNA polymerase-DNA system

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Complexes of RNA polymerase with the DNA regions protected against deoxyribonuclease digestion by the enzyme molecule (“kegs”) were obtained and studied by the method of circular dichroism (CD). The DNA within the keg consists of 20–25 base pairs and has the CD spectrum of B-form DNA. An A-like CD pattern, however, appears when the kegs start to synthesize RNA. This may be due to: (1) CD of the growing RNA chain (if it is stacked), (2) a hybrid of RNA · DNA (which is known to be in the A-form), or (3) a conformational B → A transition of the DNA template. However, the CD magnitude for the synthesizing kegs is too great for Explanation 1 to be likely.