U12 minor spliceosomal RNA is formed from U12 small nuclear (snRNA), together with U4atac/U6atac, U5, and U11 snRNAs and associated proteins, forms a spliceosome that cleaves a divergent class of low-abundance pre-mRNA introns. Although the U12 sequence is very divergent from that of U2, the two are functionally analogous.^[1]

The predicted secondary structure of U12 RNA is published,^[2]. However, the alternative single hairpin in the 3' end shown here seems to better match the alignment of divergent Drosophila melanogaster and Arabidopsis thaliana sequences.^[3] The sequences U12 introns that are spliced out are collected in a biological database called the U12 intron database.