Restriction of gene transcription by nucleotide analogs

Abstract

Summary The process of T7 DNA transcription is greatly modified when the 5′-triphosphates of formycin or 8-azaguanine are substituted for ATP or GPT, respectively. Analysis of the different steps in transcription reveals that compared with the natural purine nucleotides, a) the initiation of RNA chain by 8-azaGTP and FTP is low, b) the analogs do not inhibit the rate of chain elongation and c) enhance the efficiency of rho mediated RNA chain terminations. Transcription in the presence of rho is restricted to gene 0.3 with 8-azaGTP and genes 0.3 and 0.7 with FTP. Post-transcriptional cleavages of T7 RNA by E. coli RNase III occur at an extremely low rate with T7 RNA containing FMP residues. Although double stranded ribopolymers with 8-azaGMP residues are slowly degraded by RNAase III, cleavages of T7 RNAazag occur but generate RNAs different from what they are in the control experiment. The present findings suggest that regions between genes 0.7 and 1 and 1.1 and 1.3 are G-C rich whereas regions between early promotor and gene 0.3 and genes 1 and 1.1 are A-T rich.