Molecular Biology

Making a Copy of a Copy

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Science  24 Dec 2004:
Vol. 306, Issue 5705, pp. 2165
DOI: 10.1126/science.306.5705.2165b

MicroRNAs (miRNAs) are small noncoding RNAs that are complementary to their targets and are encoded in the genomes of most plants and animals as self- complementary fold-back precursors, which undergo processing into ∼21-nucleotide (nt) effector species. The fold-back structure of miRNA precursors suggests that miRNA genes may have evolved from inverted duplications of their target genes, and Allen et al. explore this possibility in Arabidopsis. If miRNAs arose in this manner, they should have regions of homology extending beyond the ∼21-nt complementary core. Of the 91 miRNA loci used to search the Arabidopsis genome, only miR161 and miR163 showed extended sequence similarity to their target genes and to closely related family members. Unlike other miRNA multigene families, miR161 and miR163 are represented by single genes and are not found outside Arabidopsis, supporting the idea that they might be evolutionarily recent additions. Potential evolutionary intermediates of miRNAs were also identified; one of these loci is located close to its putative targets, as are miR161 and miR163, and phlyogenetic analysis indicates that all three are related to their targets. — GR

Nature Genet. 36, 1282 (2004).

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