Fig. 6. OP-Cu footprinting of the STT. (A) In situ OP-Cu footprinting was carried out as described in Materials and methods. The thick line indicates a region of protection against OP-Cu cleavage, and arrows indicate sites of OP-Cu hypersensitivity, with the size of the arrow indicating the relative level of hypersensitivity. The terminal base of the transferred strand is defined as the +1 position and all negative numbers are base positions in the target extension. (B) A densitometric trace of the gel in (A) is shown. (C) Summary of the results of OP-Cu footprinting.