Isolation of telomerelike sequences from Cryptococcus neoformans and their use in high-efficiency transformation.

Development of a transformation system for the fungal human pathogen Cryptococcus neoformans is an important prerequisite for the identification of genes involved in virulence. It has previously been reported that low-efficiency transformation can be achieved by using the cloned C. neoformans URA5 gene and ura5 mutants. The introduction of linearized URA5 vectors into C. neoformans resulted in unstable transformants which apparently harbored linear extrachromosomal DNA molecules. In this paper, the nature of these molecules is confirmed to be linear by exonuclease digestion. Recovery of the extrachromosomal DNA in Escherichia coli and sequence analysis demonstrates that repeats characteristic of telomeric DNA have been added to the ends of the introduced DNA. The recovered plasmids are capable of transforming at much higher efficiencies either in the supercoiled state (up to 200 transformants per microgram) or the linear state (up to 90,000 transformants per microgram).