LINEAR DNA PLASMIDS FROM PICHIA-ETCHELLSII, DEBARYOMYCES-HANSENII ANDWINGEA-ROBERTSIAE

Linear DNA plasmids were found in the following yeasts: four strains o f Kluyveromyces lactis, one of Debaryomyces hansenii, one of Wingea ro bertsiae and four of Pichia etchellsii. In each case, the plasmids wer e present as a pair of DNA molecules of different sizes. The plasmids of K. lactis strains were associated with a killer activity and their structure was similar to the known killer plasmids pGKL1 and 2. The pl asmids from the other three species were different from pCKL plasmids and showed no killer activity against the yeast species tested so far. In all cases, the linear molecules possessed terminal (probably inver ted) repeats and their 5' ends had a protected structure insensitive t o lambda exonuclease, while the 3' ends were accessible to exonuclease III. All these strains could be efficiently cured of the plasmids by ultraviolet irradiation. The plasmids from D. hansenii (pDH1A and B) a nd from W. robertsiae (pWR1A and B) shared related sequences with some of the K. lactis killer plasmid genes (encoding the supposed DNA poly merases, RNA polymerase and the chitinase), suggesting related genome organization of these plasmids. The pair of plasmids from P. etchellsi i (pPE1A and B) appear to be a distantly related member of the group. This pair showed no sequence homology with other plasmids, except weak homology with the putative RNA polymerase gene of pGKL2. None of the plasmids contained the sequences homologous to ORF3 and ORF4 of pGKL1 encoding the toxin resistance determinant and the toxin gamma subunit, respectively.