Promoter upstream bent DNA activates the transcription of the Clostridium perfringens phospholipase C gene in a low temperature-dependent manner

The phospholipase C gene (plc) of Clostridium perfringens possesses three phased A-tracts forming bent DNA upstream of the promoter. An in vitro transcription assay involving C. perfringens RNA polymerase (RNAP) showed that the phased A-tracts have a stimulatory effect on the plc promoter, and that the effect is proportional to the number of A-tracts, and more prominent at lower temperature. A gel retardation assay and hydroxyl radical footprinting revealed that the phased A-tracts facilitate the formation of the RNAP-plc promoter complex through extension of the contact region. The upstream (UP) element of the Escherichia coli rrnB P1 promoter stimulated the downstream promoter activity temperature independently, differing from the phased A-tracts. When the UP element was placed upstream of the plc promoter, low temperature-dependent stimulation was observed, although this effect was less prominent than that of the phased A-tracts. These results suggest that both the phased A-tracts and UP element cause low temperature-dependent activation of the plc promoter through a similar mechanism, and that the more efficient low temperature-dependent activation by the phased A-tracts may be due to an increase in the bending angle at a lower temperature.