In molecular biology, the small nucleolar RNAs SNORD106 and SNORD12 (also known as U106 and HBII-99 respectively ) are two related snoRNAs which belongs to the C/D class of small nucleolar RNAs (snoRNAs). Both contain the conserved C (UGAUGA) and D (CUGA) box sequence motifs[1]
Human SNORD12 (HBII-99) is the homologue of mouse snoRNA MBII-99. In humans both HB11-99 and U106 snoRNAs share the same host gene.[2][3]
Most of the members of the box C/D family function in directing site-specific 2'-O-methylation of substrate RNAs. HBII-99 is predicted to guide the 2'O-ribose methylation of 28S rRNA G3878.[4] U106 contains conserved antisense elements which would predict U106 methylates residues G1536 and U1602 of 18S rRNA.[5] However, these targets do not appear to be methylated and U106 might function as an RNA chaperone during rRNA folding.[2] A similar role has been suggested for the H/ACA snoRNAs U17a and U17b[2]