The sequence of enzymatic reactions by which a 2,2,7-trimethylguanosine cap structure is added to the 5' end of an snoRNA. The snoRNA capping includes the formation of 7-methyl-G caps found on all RNA polymerase II transcripts, followed by hypermethylation at the 2' position of the guanosine residue to convert a mono-methylated cap to a 2,2,7-trimethylguanosine cap structure. Note that the pol III transcribed snoRNAs are also TMG capped.
snoRNA 2,2,7-trimethylguanosine (TMG) cap formation