A common sequence motif determines the Cajal body-specific localization of box H/ACA scaRNAs.
Post-transcriptional synthesis of 2'-O-methylated nucleotides and pseudouridines in Sm spliceosomal small nuclear RNAs takes place in the nucleoplasmic Cajal bodies and it is directed by guide RNAs (scaRNAs) that are structurally and functionally indistinguishable from small nucleolar RNAs (snoRNAs) directing rRNA modification in the nucleolus. The scaRNAs are synthesized in the nucleoplasm and specifically targeted to Cajal bodies. Here, mutational analysis of the human U85 box C/D-H/ACA scaRNA, followed by in situ localization, demonstrates that box H/ACA scaRNAs share a common Cajal body-specific localization signal, the CAB box. Two copies of the evolutionarily conserved CAB consensus (UGAG) are located in the terminal loops of the 5' and 3' hairpins of the box H/ACA domains of mammalian, Drosophila and plant scaRNAs. Upon alteration of the CAB boxes, mutant scaRNAs accumulate in the nucleolus. In turn, authentic snoRNAs can be targeted into Cajal bodies by addition of exogenous CAB box motifs. Our results indicate that scaRNAs represent an ancient group of small nuclear RNAs which are localized to Cajal bodies by an evolutionarily conserved mechanism.
Richard
Patricia
P
Laboratoire de Biologie Moléculaire Eucaryote du CNRS, UMR5099, IFR109, 118 route de Narbonne, 31062 Toulouse, France.
Darzacq
Xavier
X
Bertrand
Edouard
E
Jády
Beáta E
BE
Verheggen
Céline
C
Kiss
Tamás
T
D001483:Base Sequence; D002466:Cell Nucleolus / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D020541:Coiled Bodies / Q000737:chemistry* / Q000378:metabolism*; D016384:Consensus Sequence; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006367:HeLa Cells; D006801:Humans; D019913:Nuclear Localization Signals / Q000235:genetics; D009690:Nucleic Acid Conformation; D017434:Protein Structure, Tertiary; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020537:RNA, Small Nucleolar / Q000235:genetics / Q000378:metabolism; D017381:Spliceosomes / Q000378:metabolism
D019913:Nuclear Localization Signals; D012342:RNA, Small Nuclear; D020537:RNA, Small Nucleolar