Short RNA chains synthesized at low pH are initiated at promoter sites.

Under non optimal conditions- either with limiting substrate concentrations (1) or at low pH (2)- RNA polymerase of Escherichia coli synthesizes very short RNA chains. By sequencing one RNA species synthesized at pH 5.8 upon T7 DNA we were able to demonstrate that under these conditions transcription is initiated at a normal promoter site (here A1) but however is terminated soon afterwards at specific artificial sites not used in vivo.