Patterns of 3′ untemplated additions in Drosophila miRNAs. (Left) Scenarios for 3′ untemplated additions to the pre-miRNA versus the mature miRNA/miRNA* species. Preferred addition to the pre-miRNA hairpin is expected to be reflected in a bias for modifications of 5p species relative to 3p species. (Right) The overall frequency of 3′ additions observed on Drosophila miRNAs are U > A > C > G. For U and A additions, t-test reveals a statistically significant preference for 3p additions, consistent with a preference for pre-miRNA modifications. C additions were much less frequent but also appeared to exhibit some 3p preference. Judging 5p U or A addition frequencies relative to G additions as background suggested that mature miRNA/miRNA* species are also subject to uridylation and adenylation. The full analysis is presented in Supplemental Table S7.
