FIG. 4.

Schematic steps in transcription activation by LysR-type transcription regulators. (A) Two subunits of the regulator tetramer binds to the RBS and two other subunits bind to the ABS present on the −35 promoter region. (B and C) In the presence of an inducer, the regulatory protein shifts its interaction on the ABS to −42. By interacting with the α-CTD domain of the RNAP, it directs this to bind a so-called UP-DNA sequence motif, which is located between the RBS and ABS (B). This increases the binding affinity of RNAP for the promoter and initiates transcription (C). mRNA is drawn as a zig-zagged arrow.