Fig. 1: In silico modeling of pre-snRNA secondary structures.

a Workflow of the computational procedure to identify best representative pre-snRNA secondary structures. For detailed description, see the Methods section. b In silico predicted structures of human pre-snRNAs. Best representative secondary structures for human pre-snRNAs containing 3′ extra sequences 49, 21, 7, and 48 nucleotides for U1, U2, U4, and U5 pre-snRNAs, respectively (based on ref. ²¹). c Alternative fold of human U1 pre-snRNA with a shorter 3′ end extension. Blue circles indicate extra 3′ end extension, red circles the Sm binding site and the beige lines the Near Sm-site Structure (NSS). d Box plot of the pairwise structural distances of the predicted secondary structures for Metazoa (M), fungi (F) and protists (P). Best representative structures of metazoan pre-snRNAs are significantly closer to each other (indicated by smaller normalized tree edit distances on y-axis) than those of fungi and protist species. On each box, the central mark indicates the median, and the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively. The whiskers extend to the most extreme data points not considered outliers, and the outliers are plotted individually using the ‘+’ symbol. P-values of the two-way Student t-test are indicated in Table 1. n—number of species assayed.