Coordinated regulation of gene expression by E ... - Jacobs University

RESULTS
Addition of FIS increased the reactivity of bases T-8 and T-11 at the wild-type
promoter (lanes 1–3). Also, in the presence of FIS the permanganate reactivity for all
promoter derivatives was further increased, the tyrTS and tyrT35 mutants exhibiting a
greater response than tyrTD. These observations show that at all promoters, albeit to
varying degrees, FIS enhances the interaction with the −10 region. The formation of
initiation (open) complex at the wild-type tyrT promoter requires the presence of GTP
and CTP to allow the synthesis of the dinucleotide pppGpC [Muskhelishvili et al.,
1997]. Figure 21B shows that under these conditions enhanced permanganate reactivity
was observed at the wild-type promoter principally at positions T+3, T+4, T+10, T+26
and addition of FIS had very small, if any, effect (lanes 1–3). The reactivity at positions
+3 and +4, and possibly that at +10, corresponds to the transcription “bubble” in the
DNA. The cleavage patterns observed in the mutant promoters differ from the wild-type
in one major respect, permanganate cleavage being apparent in all of them in the −10
and/or discriminator regions. For all the mutant promoters FIS enhances cleavage
significantly suggesting that in these cases FIS can facilitate initiation complex
formation. A similar effect of FIS on the wild-type promoter has previously been
observed on a linear DNA template [Muskhelishvili et al., 1997].
57