On the Initiation of Transcription by DNA‐Dependent RNA Polymerase from Escherichia coli

It is shown that preinitiator or storage stretches on T5‐DNA are not a consequence of the existence of natural nicks in this template. Nicks do not contribute to the formation of heparinlabile and stable starters. Analysis of the number of pppA and pppG starters and their products on T7‐DNA in enzyme saturation in the presence of heparin yielded 8 stable pppA starters, all synthesizing one product from the r‐strand sedimenting with 32 S and with a molecular weight of 1.9 × 10 6 (from sedimentation rate) or 2.2 × 10 6 (from chain length). Six labile pppG starters, yielding products from the l‐strand and, in addition, two very labile pppG starters seen only in the absence of heparin, also on the l‐strand, were demonstrated. These results give further evidence for the existence of preinitiator (or storage) stretches, with another template for which no assumption about the number of reading units have to be made. The polyanion heparin is well suited for the elimination of artificial starts in vitro .