Taken together, our data provide clear examples of how one snoRNA can modify multiple nucleotides in the target region by forming two different snoRNP complexes that differ in the positioning of Nop56 and Nop1 (fibrillarin) in the complex. This is different to the normal approach taken by snoRNPs, in which two separate guide regions are used to target different nucleotides. It is clear from our data that the unique D΄ box, in particular with snR13, is evolutionarily conserved and we believe that this scenario is not just found in the S. cerevisiae snoRNAs, but will be seen in most yeasts and potentially other eukaryotes. Indeed, evidence suggests that human U24 is also capable of modifying multiple sites within one target region (25). Therefore, with minor changes to the C΄/D΄ motif box C/D snoRNPs can be adapted to increase the complexity of rRNA modification without the need for additional snoRNAs.