(A) Sequence alignment of vertebrate pre-SNORD13 homologs. Antisense regions 18S-A, 18S-B, and 18S-C are highlighted in red, C and D-box motifs involved in putative kink-turn formation in yellow, and putative stem regions in gray. The small verticle black arrow indicates the 3′ end of SNORD13 as experimentally determined by RACE analysis. (B) Proposed SNORD13 base-pairing interactions with colors coded as above. Bases written in uppercase are part of stable, fully processed SNORD13 while those written in lowercase correspond to the 3′-extension of the transient pre-SNORD13 intermediate. (C) Proposed maturation of pre-SNORD13, containing a 3′-extension which masks its 5′-antisense region, to mature SNORD13 capable of interacting with 18S rRNA.
