miRNA genes are isolated, evolutionarily conserved genomic sequences that have the capacity to form extended stem-loop structures as RNA. Shown are VISTA plots of globally aligned sequence from D. melanogaster and D. pseudoobscura, in which the degree of conservation is represented by the height of the peak. This particular region contains a conserved sequence identified in this study that adopts a stem-loop structure characteristic of known miRNAs. Expression of this sequence was confirmed by northern analysis (Table 2), and it was subsequently determined to be the fly ortholog of mammalian mir-184. Most conserved sequences do not have the ability to form extended stem-loops, as evidenced by the fold adopted by the sequence in the neighboring peak.