CeR-2/CeN21 RNA is one of the novel ncRNAs isolated from C. elegans. This is 126 nt in length and have a cap at 5 termini. The sequence and the secondary structure have no similarity to those of other ncRNAs. This RNA was expressed in most cells of the worm from the early embryonic stage to adult. In cells, CeR-2/CeN21 RNA concentrates in the nucleolus. Many small RNAs in the nucleolus are classified into a C/D snoRNA family or an H/ACA snoRNA family according to their structures. To know whether the protein components of C/D snoRNPs or H/ACA snoRNPs have any relationship to CeR-2/CeN21 RNA, fluorescence in situ hybridization was performed against the worms of which snoRNP proteins were knocked down by RNAi. When
fib-1 (fibrillalin) or Ce-
nop56 (K07C5.4), a C/D snoRNP component, was targeted by RNAi, U18 snoRNA, a C/D snoRNA, diffused into the nucleoplasm and cytoplasm. A part of U18 snoRNAs accumulated in an unknown subnuclear component, which was different from the nucleoli. U17/snR30 snoRNA, an H/ACA snoRNA, stayed in the nucleolus. When Ce-
cbf5 (K01G5.5) or Ce-
nop10 (C25A1.6), an H/ACA snoRNP protein, was targeted, most U18 snoRNAs were observed in the nucleolus but U17/snR30 snoRNA dispersed into the cytoplasm. In all cases, the localization of CeR-2/CeN21 RNA was not influenced. These results suggested that the nucleolar localization system of CeR-2/CeN21 RNA is different from those of C/D snoRNAs and H/ACA snoRNAs.