the CCAAT element from the pro- 2(I) collagen promoter. The DNA backbone is shown as ribbons (purple) with the bases displayed. The two possible locations of the CCAAT box, according to the modeling, have been colored cyan. For the right model of the NF-Y/CCAAT complex. NF-YC, NF-YB and DNA are colored as in figure on the left, whereas NF-YA is colored blue. The two alternative positions for the linker connecting NF-YA1 and NF-YA2 sub-domains are shown as blue dotted lines. Secondary structure elements of the histone pair that are implicated in NF-YA1 and NF-YA2 recognition (see text) are labeled and colored in red and gray, respectively. For clarity, only the bases for the CCAAT pentanucleotide are shown