A CIRCULAR PLASMID FROM THE YEAST TORULASPORA-DELBRUECKII

A new member of the 2-mu m family of plasmids, named pTD1, was found i n the yeast Torulaspora delbrueckii, a widespread yeast associated wit h food. Nucleotide sequences revealed the presence of a pair of invert ed repeats and three open reading frames, one of which is a homologue of the FLP recombinase gene of 2-mu m plasmid. An ARS region was ident ified, by replication in Saccharomyces cerevisiae and T. delbrueckii, near one of the inverted repeats. By the use of pTD1 derivatives and a uxotrophic mutant hosts, an efficient host-vector system was establish ed for T. delbrueckii. So far, the 2-mu m family of plasmids is restri cted to four closely related genera (Q6 group): Saccharomyces, Zygosac charomyces, Kluyveromyces, and Torulaspora. After a survey of 2500 str ains belonging to about 500 species (80 genera) of yeast, no circular plasmids were found in other genera. (C) 1997 Academic Press.