Transcription-Associated Recombination Is Dependent on Replication in Mammalian Cells

Abstract

Transcription can enhance recombination; this is a ubiquitous phenomenon from prokaryotes to higher eukaryotes. However, the mechanism of transcription-associated recombination in mammalian cells is poorly understood. Here we have developed a construct with a recombination substrate in which levels of recombination can be studied in the presence or absence of transcription. We observed a direct enhancement in recombination when transcription levels through the substrate were increased. This increase in homologous recombination following transcription is locus specific, since homologous recombination at the unrelated hprt gene is unaffected. In addition, we have shown that transcription-associated recombination involves both short-tract and long-tract gene conversions in mammalian cells, which are different from double-strand-break-induced recombination events caused by endonucleases. Transcription fails to enhance recombination in cells that are not in the S phase of the cell cycle. Furthermore, inhibition of transcription suppresses induction of recombination at stalled replication forks, suggesting that recombination may be involved in bypassing transcription during replication.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Helen Bryant for her scientific advice and discussions and Susan Newton for help with flow cytometry. We thank Graeme Smith and Stephen Trusko for materials.

The Swedish Cancer Society, the Swedish Children's Cancer Foundation, the Swedish Research Council, the Swedish Pain Relief Foundation, the Medical Research Council, and the Biological & Biotechnological Sciences Research Council supported this work financially.