Specificity of Initiation and Synthesis of RNA from DNA Templates

The DNA-dependent RNA polymerase reaction in vitro can be thought to proceed in at least three discrete stages: (1) Recognition by the polymerase of specific starting points on DNA template. These starting points on DNA may be in the form of unique nucleotide sequences and/or structurally altered sites at which the enzyme binds to the template to initiate RNA chains. (2) In the second stage the stepwise addition of ribonucleotides to the 3′-hydroxyl group of the ribonucleoside end occurs. In this process the sequence of ribonucleotides incorporated into the RNA chain is directed in a typical Watson-Crick complementary base-pairing fashion by the sequence of bases in the DNA template being transcribed. This growth of RNA chains occurs through the intermediate formation of a tertiary stable complex between DNA-RNA and enzyme (Bremer and Konrad, 1964). The rate of growth of RNA chain in vitro decreases with time until the third stage...