Biomedical Engineering Reference
In-Depth Information
Box H/ACA
snoRNA structure
Ψ
Ψ
pseudouridylation
pocket
pseudouridylation
pocket
3'
rRNA
5'
5'
ANANNA
ACA
NNN
3'
Box H
Box ACA
Fig. 13.2
Structure of an H/ACA snoRNA. Schematic representation of a box H/ACA snoRNA
containing several evolutionarily conserved structural elements including a box H (ANANNA) and
box ACA motif, a hairpin structure, and a pseudouridylation pocket (
red
). The pseudouridylation
pocket base pairs to regions in rRNA (
green
) flanking the target uridine. The modified Y residue
is illustrated in
yellow
13.3.1
H/ACA SnoRNAs
13.3.1.1
The Structure of H/ACA SnoRNAs
The box H/ACA snoRNAs are responsible for the site-specific conversion of more
than 100 uridine residues to Y on eukaryotic rRNA (Ganot et al.
1997
; Kiss et al.
2004
; Lestrade and Weber
2006
; Ni et al.
1997
). Eukaryotic H/ACA snoRNAs con-
tain several evolutionarily conserved structural elements including the box H and
box ACA motifs, a hairpin structure, and pseudouridylation pockets (Ganot et al.
1997
; Ni et al.
1997
) (Fig.
13.2
). The secondary structure of H/ACA snoRNAs
typically consists of 60-75 nucleotide-long hairpins that are linked together by a
hinge and are followed by a short tail, often referred to as a hairpin-hinge-
hairpin-tail arrangement (Bortolin et al.
1999
). The conserved box H motif lies in
the hinge connecting the two hairpins and consists of an ANANNA sequence, where
“N” is any nucleotide. The trinucleotide ACA is located approximately three nucle-
otides from the 3¢ end of the snoRNA sequence. Importantly, the target uridine on
rRNA is always positioned 14-16 nucleotides upstream of either the box H motif or
the ACA motif, a region referred to as a pseudouridylation pocket (Bortolin et al.
1999
). The pseudouridylation pocket is complementary in sequence to the 3-10
nucleotides on either side of the target uridine on rRNA. This binding arrangement
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