Function of the Genetic Material: Transposable Elements in Lower Eukaryotes

Abstract

In the past 10 years increasing evidence has been provided that eukaryotic genomes are inhabited by a variety of mobile genetic elements. The occurrence of such elements in forms of plasmids or transposons has changed our view of the eukaryotic genome in terms of its stability and its evolutionary origins quite considerably. Even though our knowledge of the spectrum of mobile elements and their occurrence in the various taxa is still limited, there is now sufficient information available on their molecular nature, their replication strategies, and their cellular function to outline some common and general features. This review will be focused on lower eukaryotes such as yeast, fungi, slime molds, and algae. Research on this group of organisms has contributed, although to a quite different degree, very much to our current knowledge on the nature of eukaryotic mobile elements. Furthermore, I will restrict this review to mobile sequences which interact physically in some way with the nuclear or extranuclear genomes. Thus, the reader is referred to the comprehensive treatise by (Berg and Howe 1989) which covers the entire field of “mobile DNA”. The presentation of material in this review is not only biased by my own research interests, but also by extreme variability in knowledge in the various systems investigated. Starting with an overview of transposons in lower eukaryotes and their possible relationship to each other and to other entities of cellular life, I will discuss the major strategies for expression of genetic information carried by transposons and for replication of the genome.