5 Transposons

Abstract

1. INTRODUCTION
The Caenorhabditis elegans genome is approximately 30 times smaller than the human genome, but it is estimated to contain only 5 times fewer genes (Wilson et al. 1994; Waterston et al., this volume). The compact worm genome results from shorter unique noncoding sequences (such as introns) and from fewer repeated sequences. It is not yet clear what role repeated sequences have in the C. elegans genome. An interesting hypothesis is that these elements are involved in meiotic recombination (La Volpe et al. 1988; Naclerio et al. 1992). Part of the repetitive DNA probably has no function for the nematode at all; it may represent parasitic or selfish DNA. In their simples form, these molecular parasites or transposons are single genes. They ensure their own spread by initiation of their own replication within genomes (see Plasterk 1993).

In this chapter, we review what is known about transposable elements in C. elegans, their mechanism of transposition, and their regulation. We discuss how transposons are used for the genetic analysis of C. elegans, and we focus on elements that have been shown to be mobile. The C. elegans genome also contains elements whose structure suggests that they are or were transposons, such as retro-element-like sequences (Britten 1995; Youngman et al. 1996); these elements are not described in detail here. Emphasis is placed on the Tc1 element, which causes the majority of gene inactivations in certain natural strains of the worm. It is also the transposon that has been studied in most...