DNA integration by Ty integrase in yku70 mutant Saccharomyces cerevisiae cells

In the present work we examined nonhomologous integration of plasmid DNA in a yku70 mutant. Ten of 14 plasmids integrated as composite elements, inclu ding Ty sequences probably originating from erroneous strand-snitching and/ or priming events. Three additional plasmids integrated via Ty integrase wi thout cointegrating Ty sequences, as inferred from 5-bp target site duplica tion and integration site preferences. Ty integrase-mediated integration of non-Ty DNA has never been observed in wild-type cells, although purified i ntegrase is capable of using non-Ty DNA as a substrate in vitro. Hence our data implicate yKu70 as the cellular function preventing integrase from acc epting non-Ty DNA as a substrate.