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. 2012 Apr 23;29(10):3153–3159. doi: 10.1093/molbev/mss122

FIG. 1.

FIG. 1.

Activation modes of the Escherichia coli cryptic bgl operon. Genes are indicated by gray arrows. (A) In wild-type cells, transcription of the bgl operon is silenced by multiple mechanisms. First, the promoter region (−35 and −10 region) is directly silenced by a nearby AT-rich DNA silencer element. Second, two rho-independent transcriptional terminators (T1 and T2) interrupt ongoing transcription (at the beginning and at the end of bglG). (B) IS insertion (dark gray box) can displace the silencer element from the bgl promoter region (−35 and −10) and allows transcription of the BglG antiterminator protein. Due to efficient antitermination by BglG in the presence of salicin, the operon is transcribed (filled, black arrows). (C) Mutations changing the CAP-binding site (starred black box) allow strong catabolic activation during carbon starvation. In addition, there are also numerous known point mutations that can activate the bgl operon. For more details, see Hall (1998) and Moorthy and Mahadevan (2002).