Poly(dA:dT) tracts track fine variations in NFR positions. (A) The class I promoters, which show a progressive narrowing of the NFR, are divided into six equal subgroups, I–VI. (B) Poly(dA:dT) tract enrichment differences for each subgroup. Arrows denote locations of symmetric axes for individual subgroups. (C) Schematic summary of the locations of six promoter elements in each promoter subgroup. Slopes are derived by linear regression and represent the average number of base pairs an element shifts per subgroup of promoters. (D) Plot of NFR center coordinates versus poly(dA:dT) intercept coordinates. Multiple points for each subgroup represent intercepts for different tract length.
