Cointegration of transforming DNAs in Aspergillus nidulans: a model using autonomously-replicating plasmids.

Transforming DNAs form cointegrates in Aspergillus nidulans by homologous and non-homologous recombination as well as by end-to-end ligation of linear fragments. This process has been studied by means of a model in which the linkage of a marker gene to the origin of autonomous replication AMA1 was selected for. Recombinant plasmids were rescued into Escherichia coli and subjected to restriction mapping and sequence analysis. It was shown that circular DNA molecules recombined predominantly within homologous fragments. Linear DNA fragments integrated into circular plasmids by invasion of their ends into random non-homologous sites, but exhibited some bias in choice of a target sequence. Cointegrates of multiple plasmid copies were often observed. In some of the plasmids analysed, short duplications of the target sequence flanking an inserted linear DNA fragment have been revealed.