DNaseI footprinting of archaeal TBP and TFB on the template strand of negatively supercoiled (σ = −0.053) 16S (lanes 1–7) and positively supercoiled (σ = +0.047) 16S templates (lanes 8–13). Lane 1 contains a ddA sequencing ladder. Reactions contain 0 pmol (lanes 2 and 8), 3 pmol (lanes 3 and 9), 1.5 pmol (lanes 4 and 10), 0.75 pmol (lanes 5 and 11), 0.38 pmol (lanes 6 and 12), and 0.19 pmol (lanes 7 and 13) of an equimolar mix of TBP and TFB. The region protected from cleavage by DNaseI is indicated by an open box; the TATA and initiator elements are shown as filled boxes.