Analysis of bulges found in human miRNAs. (a) the occurrences of 5’ bulge U’s with different closing base pair combinations. (b) the number of 1-nucleotide 5’ bulges with different closing base pair combinations found in human miRNA hairpin precursors. The most frequently occurring closing base pair combination was determined for each 1-nucleotide bulge, and then calculated for all others. Each closing base pair combination has a unique color, which is applied to each type of bulge. (c) the directionality of the motif (5’ bulge vs. 3’ bulge) influences preference of closing base pairs.