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A
3
G
U
C
G
Y
U
Y
R
W
R
A
C
C
U
C
G
G
C
R
A
G
Y
U
Y
Y
N
R
R
R
G
G
R
N
Y
Y
Y
C
Y
P2
P1
U
G
G
5
HO
P3
G
G
C
C
U CG U
P1.1
A
R
U
C
J4/2
R
U
G
C
Y
A
R
N
N
R
A
Y
G
R
U
Y
N
N
U Y
P4
B
28S rDNA
R2 retrotransposon
28S rDNA
5
3
5
5 UTR
ORF
3 UTR
3
5
3
28S rDNA
6
1
R2 protein
3'
R2 retrotransposon
5
5'
28S rRNA
28S rRNA
3
5
3
2
5
5
3
28S rDNA
R2 protein
R2 retrotransposon
3
5
3
3
5
5
HO
3
4
28S rDNA
R2 protein
5
3
3
5
HO
Figure 4.8 (A) The consensus sequence and secondary structure for the Drosophila R2
ribozymes with IUPAC nucleotide abbreviations. (B) The R2 retrotransposition event. R2
DNA is (1) cotranscribed from the 28S ribosomal locus (rDNA) to yield the ribozyme-
containing R2 RNA embedded in the 28S rRNA. The R2 retrotransposon is then (2)
excised from the surrounding transcript at the 5 0 junction via the action of the HDV-like
ribozyme that will cleave the RNA at the position marked with a red star and at the 3 0
junction by unknown factors. Following terminal processing, the R2 RNA is (3) translated
(Continued)
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