FIG. 5.

DNase I footprint assay of CodY interaction with the citB regulatory region. A 523-bp PCR product, corresponding to positions −320 to +202 with respect to the citB transcriptional start site and labeled at the 5′ end of the template (noncoding) strand, was incubated with increasing amounts of purified CodY-His₆ in the presence or absence of 2 mM GTP. After treatment with DNase I, the DNA was denatured and subjected to electrophoresis. A set of Sanger sequencing reactions (not shown) were primed with the same oligonucleotide used for synthesis of the template strand of the PCR product and used to establish the positions of the protected bands. Vertical lines on the left indicate regions protected by CodY.