LINEAR DNA PLASMIDS OF YEASTS

Linear DNA plasmids are common among filamentous fungi and plants in w hich they are generally associated with mitochondria. In contrast, the linear DNA plasmids of yeasts appear to be cytoplasmic and to have a specific genetic organization. In these respects the yeast linear plas mids can be regarded as a separate group of plasmids. A survey of plas mids among about 1800 strains covering practically all the currently a ccepted species of yeast (about 600) has provided a preliminary, overa ll view of the nature and frequency of yeast plasmids. Linear DNA plas mids were found at a frequency of 1-2%, with more than 20 cases of new linear plasmids discovered in a large variety of species. The same su rvey showed that circular DNA plasmids are characteristically confined to a few genera and species. The linear DNAs have many features in co mmon with the linear killer DNAs of Kluyveromyces lactis and form a la rge family of multicopy, small DNAs disseminated among yeast species.