Positive screening and transformation of ura5 mutants in the fungus Podospora anserina: characterization of the transformants.

To develop a transformation system in the filamentous fungus Podospora anserina we have selected ura5 mutants deficient in orotidylic acid pyrophosphorylase using a positive screening. These mutants could be transformed to prototrophy by an hybrid vector carrying the ura5 gene of this organism. The properties of the transformants have been analysed. In most cases integration of the transforming vector occurred outside the ura5 locus and frequently repeated tandem copies of the vector were found. Reversion of the transformants could also be selected and we found that it can occur by exact or only partial excision of the integrated vector.