Proposed secondary structure of eukaryotic U14 snRNA.

U14 snRNA is a small nuclear RNA that plays a role in the processing of eukaryotic ribosomal RNA. We have investigated the folded structure of this snRNA species using comparative analysis of evolutionarily diverse U14 snRNA primary sequences coupled with nuclease digestion analysis of mouse U14 snRNA. Covariant nucleotide analysis of aligned mouse, rat, human, and yeast U14 snRNA primary sequences suggested a basic folding pattern in which the 5' and 3' termini of all U14 snRNAs were base-paired. Subsequent digestion of mouse U14 snRNA with mung bean (single-strand-specific), T2 (single-strand-preferential), and V1 (double-strand-specific) nucleases defined the major and minor cleavage sites for each nuclease. This digestion data was then utilized in concert with the comparative sequence analysis of aligned U14 snRNA primary sequences to refine the secondary structure model suggested by computer-predicted folding. The proposed secondary structure of U14 snRNA is comprised of three major hairpin/helical regions which includes the helix of base-paired 5' and 3' termini. Strict and semiconservative covariation of specific base-pairs within two of the three major helices, as well as nucleotide changes that strengthen or extend base-paired regions, support this folded conformation as the evolutionary conserved secondary structure for U14 snRNA.