Bacteriophage Mu integration in yeast and mammalian genomes

Genomic parasites have evolved distinctive lifestyles to optimize replication in the context of the genomes they inhabit. Here, we introduced new DNA into eukaryotic cells using bacteriophage Mu DNA trans- position complexes, termed 'transpososomes'. Following electroporation of transpososomes and selection for marker gene expression, efficient integration was verified in yeast, mouse and human genomes. Although Mu has evolved in prokaryotes, strong biases were seen in the target site distribu- tions in eukaryotic genomes, and these biases differed between yeast and mammals. In Saccharo- myces cerevisiae transposons accumulated outside of genes, consistent with selection against gene dis- ruption. In mouse and human cells, transposons accumulated within genes, which previous work suggests is a favorable location for efficient expres- sionofselectablemarkers.Naturallyoccurringtrans- posons and viruses in yeast and mammals show related, but more extreme, targeting biases, sug- gesting that they are responding to the same pres- sures. These data help clarify the constraints exerted by genome structure on genomic parasites, and illustrate the wide utility of the Mu transpososome technology for gene transfer in eukaryotic cells.