Regulatory Role of Small Nucleolar RNAs in Human Diseases

Stepanov, Grigory A.; Filippova, Julia A.; Komissarov, Andrey B.; Kuligina, Elena V.; Richter, Vladimir A.; Semenov, Dmitry V.

Eukaryotic box C/D RNAs are typically 70-120 nt in length and contain two conserved elements: boxes b (PuU-GAUGA) and D (CUGA) located at the 5 -and 3termini of the RNA molecule, respectively (Figure 1(a) ). These sequence elements form so-called "kink-turn" (stembulge-stem) structure that serves as the scaffold for the assembly of a small nucleolar ribonucleoprotein (snoRNP) including the following proteins: Nop1p (also known as fibrillarin), Nop56p, Nop58p, and Snu13p (15.5 kDa) [3] [4] [5] [6] . Methyltransferase fibrillarin serves as the key component of snoRNPs: it catalyzes the transfer of a methyl group from S-adenosylmethionine (SAM) to 2 -O-position of the target nucleotide. The methylation guide sequence exhibits complementarity to the region of the target RNA; it is 10-21 nt long and located upstream of the box D/D motifs. The base in the target RNA paired to the fifth nucleotide upstream of the box D/D sequence is to be methylated [1, 7] .