Editing of miR-1 occurs within the seed region and affects binding to mRNA targets. (A) Nucleotide modification at position 4 is shown for miR-1. An adenine to guanine (A:G) change was observed in UT-7, representing 23 of 2306 total miR-1 reads (Table 4). The effect of A:G edit at position 4 (4A:G) on mRNA target specificity is illustrated by comparing select miR-1 and miR-1 (4A:G) targets. The predicted targets for miR-1 (4A:G) are entirely different compared with the unedited miR-1. (B) Shown is a sequence alignment of miR-1 (wild-type and edited) and its binding sites in the 3′-UTR of MEIS1 (position 160-181) and TP53 (position 654-672). The miRNA-mRNA binding energy score (in kcal/mol) was determined for each pairing and shown on the right. The * indicates the binding energy score for a second miR-1 binding site in the TP53 UTR (position 689-698). (C) Luciferase activity was measured for MEIS1-UTR and TP53-UTR luciferase reporters in the presence of miR-1, miR-1 (4A:G), or vector control. Shown are relative values of 2 independent experiments performed in triplicate.