Mouse embryonic stem cells exhibit high levels of extrachromosomal homologous recombination in a chloramphenicol acetyltransferase assay system.

Mouse embryonic stem (ES) cells were compared to COS1 and CV1 cells for their ability to perform extrachromosomal homologous recombination. RSVCAT plasmid substrates consisting of overlapping chloramphenicol acetyltransferase (CAT) gene fragments were transiently transfected into cells and extracts were assayed for CAT activity. Approximately 10% activity, relative to transfection with a complete CAT gene, was recovered for the recombination substrates in each of the cell lines tested. ES cells, therefore, as other cell lines, are capable of high levels of extrachromosomal recombination.