Many C/D box snoRNA also contain an additional less-well-conserved copy of the C and D motifs (referred to as C' and D') located in the central portion of the snoRNA molecule.
Moitos snoRNA de caixa C/D conteñen tamén unha copia adicional menos conservada dos motivos C e D (denominada C' e D') situada na porción central da molécula de snoRNA.