Linear DNA Plasmids and Killer System of Kluyveromyces lactis

Abstract

Plasmids were originally defined as covalently closed circular DNAs replicating outside the chro- mosome. Indeed, the first eukaryotic plasmid, 2µm DNA of Saccharomyces cerevisiae (Sinclair et al. 1967), and the subsequent fungal p1DNA of Podospora anserina (Stahl et al. 1978), were a circular type. This definition, however, was dispelled by the discoveries of mitochondrial linear S plasmids from Zea mays (Pring et al. 1977), the cytoplasmic linear pGKL plasmids from the dairy yeast Kluyveromyces lactis (Gunge et al. 1981; Wesolowski et al. 1982a), and the mitochondrial linear pAl from the fungus Ascobolus immersus (Francou 1981). The linear plasmids, thought to be rare in the early 1980s (Esser et al. 1986), now have a great distribution in eukaryotes, outnumbering circular ones, even in bacteria (Meinhardt et al. 1990, 1997). There is a parallel with the discoveries of mitochondrial genomes: in discord with the earlier belief of circular DNA, a number of linear mitochondrial genomes have been isolated from yeasts including Candida spp., Pichia spp., and Williopsis (Hansenula) spp. as well as from the cilata protozoan Tetrahymena spp. (Nosek et al. 1998). This chapter deals with our recent knowledge of the molecular biology of yeast DNA linear plasmids. A series of related review articles have been published (Gunge 1986, 1988, 1995; Volkert et al. 1989; Stark et al. 1990; Meinhardt et al. 1990; Meinhardt and Rohe 1993; Fukuhara 1995; Magliani et al. 1997; Schaffrath and Breunig 2000; Meinhardt and Schaffrath 2001).