Activity of a plasmid-borne leu-500 promoter depends on the transcription and translation of an adjacent gene.
leu-500 is a chromosomal promoter mutation in Salmonella typhimurium that normally causes the promoter to be inactive in the initiation of RNA synthesis. But in a strain that has mutations in topA, the gene encoding DNA topoisomerase I, the mutant promoter becomes active. We show that the leu-500 promoter can function on a plasmid when it is adjacent to the tetracycline-resistance gene tetA. Activation of the leu-500 promoter requires that the tetA gene is transcribed and translated and that the host cell is topA. We propose that the A----G mutation in the -10 region of the leu-500 promoter is compensated by local negative supercoiling arising from transcription of the tetA gene, which may reach elevated levels in a topA background, provided that diffusional dissipation is reduced due to anchoring of the TetA peptide in the membrane. This is a clear example of the modulation of the activity of a promoter by the activity of another promoter in cis, when they can be coupled through the topology of the template.
Chen
D
D
Department of Biochemistry, University, Dundee, United Kingdom.
Bowater
R
R
Dorman
C J
CJ
Lilley
D M
DM
D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004278:DNA, Superhelical / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007930:Leucine; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D012486:Salmonella typhimurium / Q000235:genetics*; D013753:Tetracycline Resistance; D014158:Transcription, Genetic
D004278:DNA, Superhelical; D004264:DNA Topoisomerases, Type I; D007930:Leucine