Poly(dA:dT) tract enrichment patterns in yeast promoters. (A) Poly(dA:dT) tract frequencies in class I and class II promoters are represented as relative percent enrichments over background tract frequencies. Tracts in the two orientations are considered separately and referenced as either poly(dA) or poly(dT) according to the downstream direction of transcription. Data are smoothed over 21-bp windows. Tracts of lengths 6 and greater were considered collectively for statistical accuracy. Coordinates are relative to transcription start sites (TSS). (B) Enrichment differences between poly(dA) and poly(dT) tracts as a function of promoter position; values above the x-axis indicate greater poly(dA) enrichment. The symmetric axis near −75 is indicated with a dashed line. (C) Illustrating the 180° rotational (i.e., C2) symmetry of poly(dA:dT) tracts with respect to the symmetric axis.
