(A) Three- and four-segment DNA constructs (22, 24) used for the A-tract phasing analyses of DNA bending and twisting in the complex with p53 tetramer. The spacer S3 is variable, whereas the segments S1, S2, and S4 have fixed lengths. (B) Scheme for calculation of the DNA bend angle in the three-segment construct in A. P stands for the p53-bound end of DNA and A is for the A-tract end. C denotes the center of the horizontal fragment, so that s = S3/2, dp = S2, and da = S4.