Saccharomyces cerevisiae U14 small nuclear RNA has little secondary structure and appears to be produced by post-transcriptional processing

Abstract

Yeast U14 small nuclear (sn) RNA is required for normal processing of rRNA. The sequence and folding properties of U14 were analyzed in the present study, with the aim of defining the structures of natural U14 subspecies and characterizing the folding properties of free U14 RNA. Natural U14 was determined to consist of four subspecies of 125-128 nucleotides, none containing a 5'-cap structure. Length heterogeneity occurs at both ends and is presumed to reflect post-transcriptional processing of U14 precursors. Results from nuclease and chemical probing revealed that U14 has surprisingly little secondary structure overall. Three essential sequence elements conserved among all U14 RNAs occur in regions that are largely single-stranded, i.e. box C, box D, and a 13-nucleotide segment complementary to 18 S rRNA; a non-essential 14-nucleotide sequence complementary to 18 S rRNA is also unpaired. Two non-conserved segments required for activity are part of a stably folded 32-base domain that is unique to yeast U14. Finally, a 5'-, 3'-stem shown earlier to be required for U14 accumulation appears to exist only in precursors to U14 and not in protein-free mature RNA. The implications of these results are discussed in terms of U14 synthesis and function.