Alternatively Spliced Genes
131
I.
II.
U6
U6atac
U1
U11
U12
U12
U2
U2
(b)
Fig. 3
Sequences of human spliceosomal UsnRNAs andtheir interactions with splice sites. Panel(a) Sequences and secondary structures of
spliceosomal snRNAs: U1, U2, U4/6 (for the U2 type), and U11, U12, U4atac/U6atac snRNA (for the U12 type) as well as U5snRNAs (for both classes).
The 5
0
to 3
0
orientation of U4 and U4atac is from right to left, and that of U1, U11, U2, U12, and U5snRNAs is from left to right. The RNA helices are
indicated by Roman numerals, and nucleotide positions by Arabic numerals. The shaded nucleotides are binding sites for Sm proteins, and regions
marked with black lines form base-pairing interactions with the pre-mRNA.(ModiFed with permission from Burge, C.B., Tuschl, T.H., Sharp, P.A. (1999).
in: The RNA World, Gesteland, R.±., Cech, T.R., Atkins, J.±. (Eds)
The RNA World
, Cold Spring Harbor Laboratory Press, New York, pp. 525–560.) Panel
(b) Base-pairing interactions in the U2 and U12 types of spliceosome. The exon-intron boundaries at 5
0
splice sites are marked by arrowheads. During
early stages of spliceosome assembly, U1 or U11snRNP interacts with the 5
0
splice site, and U2 or U12snRNP with the branch sites. These interactions
are displaced in mature spliceosome by U6 or U6atac associated with U2 and U12 respectively. In these drawings, the distances between interacting
nucleotides do not reflect corresponding physical distances in the spliceosome. (Adapted from Tarn, W.Y., Steitz, J.A. (1996b) Highly diverged U4 and
U6 small nuclear RNAs required for splicing rare AT-AC introns,
Science
273
(5283), 1824–1832.)
previous page 131 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online next page 133 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online Home Toggle text on/off