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. Author manuscript; available in PMC: 2021 May 1.
Published in final edited form as: Nat Rev Genet. 2020 Jul 14;21(11):699–714. doi: 10.1038/s41576-020-0254-8

Figure 5 |. Transcription unit and operon schematic.

Figure 5 |

a | When different transcription start sites (TSSs) from the same promoter are not differentially regulated, they form a single transcription unit that is limited by, but not including, a single promoter and a single terminator. b | Schematic of the gadAXW complex operon. Several internal promoters and terminators enable different sets of genes to be co-transcribed in different combinations: gadAX by the gadAp promoter; gadX and gadXW by the gadXp promoter, and gadW by the gadWp1 and gadWp2 (not shown) promoters. Red wavy lines represent mRNAs. These promoters are subject to regulation by different sets of TFs (not shown), so they are not all subject to the same signals. There are at least four operons in RegulonDB with no evidence of a single polycistronic transcript including all the genes of the operon.