Motifs around conserved proximal and distal PASs. (A) Nucleotide frequency around (±100 nt) conserved proximal and distal PASs. (B) Z_oe versus Z_dp for tetramers in four regions around the PAS. The four regions are indicated. Z_oe and Z_dp greater than 3.6 were used to define significantly biased tetramers. Tetramers with significant Z_oe are highlighted, with those biased to distal PASs in red, those biased to proximal PASs in blue, and others in black. The top five tetramers in each category are listed. (C) Summary of B. The darkness of each box reflects its level of enrichment, highlighting the difference between proximal and distal PASs. (D) PSE (left) and mean RPM (right) of first, middle, and last PASs of 3′ UTRs (all mammal conserved). (E) Sequence motifs at the cleavage site, shown as sequence logos. Two scenarios are considered, as illustrated above the logos. (Left) Cleavage site is considered to be immediately after a non-A nucleoside (shown as B) and before an adenosine. (Right) Cleavage site is considered to be immediately after an adenosine and before a B.