Electron microscopic visualization of trp operon expression in Salmonella typhimurium.
Transcriptional activity of plasmids carrying wild-type and mutant trp operons was visualized in cell lysates of Salmonella typhimurium. Plasmid and transcription-unit sizes varied with the size of the cloned operon. Following 3-(3-indolyl)acrylic acid derepression, all operons of a particular type exhibited the same high level of transcriptional activity. An estimated 11-14 transcripts must be initiated each minute to maintain the 190-base-pair spacing of RNA polymerases observed on the promoter-proximal half of the wild-type trp operon. A decline in RNA polymerase density was observed on promoter-distal portions of cloned trp operons, which may be attributable to premature transcription termination accompanying translation inhibition due to indolylacrylic acid's interference with normal tryptophanyl-tRNA synthetase activity.
D002872:Chromosome Deletion; D002876:Chromosomes, Bacterial / Q000648:ultrastructure; D004274:DNA, Recombinant / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D005798:Genes, Bacterial; D008854:Microscopy, Electron; D009876:Operon; D010957:Plasmids; D012486:Salmonella typhimurium / Q000235:genetics*; D014158:Transcription, Genetic
D004274:DNA, Recombinant; D012321:DNA-Directed RNA Polymerases