The box C/D motif directs snoRNA 5'-cap hypermethylation.
The 5'-cap structure of most spliceosomal small nuclear RNAs (snRNAs) and certain small nucleolar RNAs (snoRNAs) undergoes hypermethylation from a 7-methylguanosine to a 2,2, 7-trimethylguanosine structure. 5'-Cap hypermethylation of snRNAs is dependent upon a conserved sequence element known as the Sm site common to most snRNAs. Here we have performed a mutational analysis of U3 and U14 to determine the cis-acting sequences required for 5'-cap hypermethylation of Box C/D snoRNAs. We have found that both the conserved sequence elements Box C (termed C' in U3) and Box D are necessary for cap hypermethylation. Furthermore, the terminal stem structure that is formed by sequences that flank Box C (C' in U3) and Box D is also required. However, mutation of other conserved sequences has no effect on hypermethylation of the cap. Finally, the analysis of fragments of U3 and U14 RNAs indicates that the Box C/D motif, including Box C (C' in U3), Box D and the terminal stem, is capable of directing cap hypermethylation. Thus, the Box C/D motif, which is important for snoRNA processing, stability, nuclear retention, protein binding, nucleolar localization and function, is also necessary and sufficient for cap hypermethylation of these RNAs.
Speckmann
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Department of Biochemistry and Molecular Biology, Life Science Building, University of Georgia, Athens, GA 30602, USA.
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D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D019175:DNA Methylation; D005260:Female; D008958:Models, Molecular; D009154:Mutation; D009865:Oocytes; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability; D020537:RNA, Small Nucleolar / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D014981:Xenopus
D012315:RNA Caps; D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar