Non-homologous integration of transforming vectors in the fungus Podospora anserina: sequences of junctions at the integration sites.

Transformation of the ura5-6 mutant strain of Podospora anserina with a recombinant vector carrying the ura5+ gene often results in the integration of the transforming plasmid by non-homologous recombination outside of the genomic ura5 locus. To investigate the mechanism of such integration, we rescued the integrated plasmid from three transformants. In two cases, the rescued plasmid was highly altered compared with the original transforming vector. We cloned the junctions between plasmidic DNA and genomic DNA of the transformants and determined their nucleotide sequences. It was found that there was little homology between plasmidic and genomic DNA sequences. Moreover, in all cases deletions of plasmid sequences at the integration site had occurred. These rearrangements can be explained by the formation of multimeric plasmids prior to integration.