RNA 2'O-methylation is a frequent modification of rRNA and tRNA and supposed to influence RNA folding and stability Ribonucleoprotein (RNP) complexes, containing the proteins Nop5, L7A, fibrillarin, and a box C/D sRNA. are guided for 2'O-methylation by interactions of their RNA component with their target RNA In vitro complex assembly was analyzed for several thermophilic Archaea but in vivo studies are rare, even unavailable for halophilic Archaea To analyze the putative box C/D RNP complex in the extremely halophilic Halobacterium salinarum NRC-1 we performed pull-clown analysis and identified the proteins Nop5, L7A, and fibrillarin and the tRNA(Trp) intron, as a typical box C/D sRNA of this RNP complex in vivo. We show for the first time a ribonucleolytic activity of the purified RNP complex proteins, as well as for the RNP complex containing pull-down fractions. Furthermore, we identified a novel RNA (OE4630R-3'sRNA) as part of the complex, containing the typical boxes C/D and C'/D' sequence motifs and being twice as abundant as the tRNA(Trp) intron (C) 2010 Elsevier Inc All rights reserved