Asymmetric RNA synthesis in vitro: heterologous DNA-enzyme systems; E. coli RNA polymerase.

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Abstract
Current understanding of asymmetric RNA synthesis stands broadly as follows: the asymmetric in vitro synthesis of RNA can be shown to occur in a considerable variety of systems not limited by homology. Like its in vivo counterpart, it involves the interaction of enzyme with limited numbers of initiation sites on DNA templates. However, in no instance, thus far, has the identity of these initiation loci in corresponding in vitro and in vivo systems been established. The ordering of the DNA secondary structure is essential for this restricted synthesis. Evidently, base interactions in the DNA double helix modulate the DNA-enzyme interactions, so as to restrict the initiation of RNA polymerization. These template-enzyme interactions are also sensitive to changes in the protein, more sensitive, in the E. coli system, than the polymerase activity itself. The precise mechanism remains to be elucidated.