Fraction of total sites observed in the upstream 1000 nts mapped as a function of distance from the start site of the 41 known muscle (▪) and 2000 random genes (□) in C. elegans. Averages over the gene sets are shown. Motifs 1 (i), motif 2 (ii), motif 3 (iii), and combined frequency of motifs 1, 2, and 3 (iv).