6 RNA Processing and Gene Structure

Abstract

I. INTRODUCTION
The emphasis in this chapter is on various aspects of the basic molecular biology of information transfer in Caenorhabditis elegans. Overall, the genes of C. elegans have characteristics that are quite similar to those of other animals. In broad outline, the mechanisms involved in transcription, RNA processing, and translation of messenger RNA are shared with those of other animals. However, some aspects are not shared by the yeast, fly, plant, and vertebrate model organisms. Here, we briefly outline the major features of RNA processing that are shared by all of these systems (for recent reviews, see Moore et al. 1993; Madhani and Guthrie 1994) and then concentrate on aspects that make the C. elegans system especially interesting (for recent reviews, see Nilsen 1993; Blumenthal 1995; Davis 1996).

A. The Splicing Process
Genes are composed of alternating exons and introns. When these are transcribed to make pre-mRNAs, the intron sequences are removed, and adjacent exon sequences are spliced together. RNA splicing is catalyzed by a large complex of RNAs and proteins called the spliceosome, components of which recognize and cleave the 5′ and 3′ends of each intron and catalyze the joining of the exons. At the 3′ end of the gene, RNA polymerase proceeds past the end of the last exon, but the RNA is cleaved at this point, and the 3′ end of the mRNA is matured by the addition of a poly(A) sequence, which is not represented in the gene. Collectively, these events are known as pre-mRNA...