Transformation of Ustilago maydis by a plasmid containing yeast 2-micron DNA.

U. maydis has been transformed to aminoglycoside antibiotic resistance by plasmid pMP81 DNA, which contains the yeast LEU-2 gene and 2-micron DNA inserted into pCRI, encoding a gene for an aminoglycoside phosphotransferase. The resistant phenotype of transformants is mitotically unstable in the absence of antibiotics. Closed, circular pMP81 DNA was detected in transformant DNA preparations by hybridization to pCR1 DNA and by transformation of Escherichia coli to kanamycin resistance. Plasmid pMP81 DNA recovered from the transformant was not rearranged at the gross sequence level as a result of transmission in U. maydis. Preliminary evidence suggests that the yeast 2-micron DNA promotes autonomous plasmid replication in U. maydis, albeit inefficiently, resulting in low transformation frequencies and plasmid copy numbers.