RNA modification is a dynamic process which occurs under the function of some enzymes whose action is similar to that of "writers". RNA modifications are placed under 3 groups, namely methylation that contains ribosomal methylation, base methylation and mixed methylation, pseudouridine and hypoxanthine respectively.
The overview of RNA modification sites guided by enzymes as follows:
C/D box snoRNAs
The C/D box snoRNAs carry two conserved boxes, C box with 'RUGAUGA' in 5' end and D box with 'CUGA' in 3' end. While C'/D' box, the copies of C/D box are usually inside snoRNAs.
C/D box snoRNA binds to proteins to form complexes, snoRNPs, that catalyze RNA modifications. These proteins include FBL, NOP56, NOP5/NOP58 and NHPX. C/D box snoRNAs guide 2'-O-ribose methylation of target RNAs by upstream components of D/D' box.
H/ACA box snoRNAs
The H/ACA box snoRNAs contain two hairpins and two single-stranded regions. The single-stranded regions contain H box with 'ANANNA' internally and ACA box with 'ACA' in 3' end. While the bulges of hairpins bind to target RNA and guide pseudouridine modification of specific loci.
H/ACA box snoRNA binds to four proteins, including dyskerin, GAR1, NHP2 and NOP10 to guide pseudouridine methylation of target RNAs.
Cajal body-specific scaRNAs
The Cajal body-specific scaRNAs have more complex chemical structure that offen contain both C/D box and H/ACA box. They can guide modifications of snRNA, like U1, U2, U4 and U5 that transcribed by polymerase II.
The overview of RNA modification sites guided by snoRNAs as follows: