We have also shown that the combination of the unusual C΄/D΄ motif together with the extra base-pairing function together to target the two adjacent nucleotides (L2280 and L2281) in the 25S rRNA by snR13. The extra base-pairing interaction, with it overlapping with the guide region, could also influence the structure of the complex as well as increasing the efficiency of rRNA methylation. However, we have found several instances of overlap between guide and extra-base-pairing interactions in snoRNAs that modify a single site. Extra base-pairing clearly enhances modification at both sites, although the reason why modification at L2281 is more dependent on this than 2΄-O-methylation at L2280 is unclear.