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 p hased A-tracts forming bent DNA upstream of the promoter. An in vitro trans cription assay involving C.perfringens RNA polymerase (RNAP) showed that th e phased A-tracts have a stimulatory effect on the pie promoter, and that t he effect is proportional to the number of A-tracts, and more prominent at lower temperature. A gel retardation assay and hydroxyl radical footprintin g revealed that the phased A-tracts facilitate the formation of the RNAP-pl c promoter complex through extension of the contact region. The upstream (U P) element of the Escherichia coli rrnB P1 promoter stimulated the downstre am promoter activity temperature independently, differing from the phased A -tracts. When the UP element was placed upstream of the pie promoter, low t emperature-dependent stimulation was observed, although this effect was les s prominent than that of the phased A-tracts. These results suggest that bo th the phased A-tracts and UP element cause low temperature-dependent activ ation of the plc promoter through a similar mechanism, and that the more ef ficient low temperature-dependent activation by the phased A-tracts may be due to an increase in the bending angle at a lower temperature.