FIG. 4.

Spatial flexibility in cooperative DNA binding by Fli1 and Fos-Jun. (A) Alignment of the tandem Ets and AP-1 sites from the indicated promoters. In each case, the Ets site is placed 5′ to facilitate the alignment, although in some cases this represents the anticoding strand. (B) Gel shift assays performed with probes corresponding to the tandem elements with the indicated spacings. The 1-nucleotide spacing was from the UPP promoter, the 6-nucleotide spacing was a 5-nucleotide deletion from the human collagenase promoter, the 11-nucleotide spacing was from the human collagenase promoter, the 16-nucleotide spacing was a 5-nucleotide insertion into the human collagenase promoter, and the 22-nucleotide spacing was from the mouse collagenase promoter. (C) The concentration dependence of Fli1 binding to the different probes in the presence and absence of Fos-Jun is plotted. Details of the plots are as described in the legend to Fig. 3C.