Endogenous sRNA populations are overrepresented by purine rich sequences but miRNAs do not show this bias. A. Distribution of purine rich and pyrimidine rich papaya sRNA population. The reads above zero are rich in purine and below zero are rich in pyrimidine. B. Weblogo representation of randomly picked 10,000 sRNA reads of 21nt and 24nt. The Y-axis represents the bit score, which can be a maximum of 4 for complete conservation of a nucleotide. The letter on the top is present highest in the sample. C. Distribution of purine and pyrimidine in annotated miRNAs from miRBASE in 4 species (Arabidopsis thaliana, Medicago truncatula, Populous trichocarpa, Oriza sativa, and Carica papaya).