Biology Reference
In-Depth Information
CHAPTER 7
RNA Processing in C. elegans
J. Jason Morton and Thomas Blumenthal
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder,
Colorado, USA
Abstract
I. Introduction
II. RNA Processing in Other Organisms
A. Eukaryotic Pre-mRNA Processing
B. Operons
III. RNA Processing in C. elegans
A. Intron Splicing
B. Trans-Splicing
C. Operons
D. 3
0
End Formation
Acknowledgments
References
Abstract
In Caenorhabditis elegans, newly transcribed RNA is processed in several novel
ways. Although introns are removed by a canonical spliceosome, they have evolved
several specialized features that reflect the differences in the way they are recognized
and the way they are spliced. C. elegans introns are unusually short, in part because
they have no specific branch-point sequences and contain minimal polypryimidine
tracts. Instead, their 3
0
splice site is characterized by a highly conserved consensus
sequence, which alone may be sufficient to position all spliceosomal elements at the
3
0
end of the intron. Many RNA molecules are also trans-spliced: a capped 22 nt
RNA leader is donated by one of a family of specialized snRNPs and spliced to an
unpaired 3
0
splice site, usually just upstream of the start codon. The RNA upstream
of this splice site, the outron, is removed during trans-splicing and presumably
degraded, making the identification of the transcriptional start site problematic.
Transcripts from approximately 70% of all genes are trans-spliced. Trans-splicing
has enabled the evolution of operons - multigene clusters in which a single upstream
promoter drives the transcription of a polycistronic pre-mRNA. The C. elegans
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