The NOP1 component of box C/D small nucleolar ribonucleoprotein complexes (snoRNPs) methylates the 2' position of the ribose moiety of nucleotides in precursor ribosomal RNA (pre-rRNA) (Kiss-Laszlo et al. 1996, Galardi et al. 2002). Box C/D snoRNPs contain NOP1 (homologous to Fibrillarin in humans), NOP56, NOP58 (NOP5), SNU13 (homologous to 15.5K, NHP2L1 in humans), and a box C/D snoRNA, which guides the snoRNP to the site of methylation by base pairing with 10-21 nucleotides of the pre-rRNA (Schimmang et al. 1989, Kiss-Laszlo et al. 1998, Wu et al. 1998, Lafontaine and Tollervey 1999, Lafontaine and Tollervey 2000, Watkins et al. 2000, Galardi et al. 2002).