Xenopus cell-free extracts to study the DNA damage response.

Cell-free systems derived from Xenopus eggs represent a powerful tool, intermediate between in vitro and in vivo model systems. Here, we describe protocols to prepare cell-free extracts recapitulating several aspects of the DNA damage response, including the DNA damage-dependent activation of ATM/ATR protein kinases and several DNA damage checkpoint signaling pathways that inhibit initiation of DNA replication. We provide protocols to prepare cell-free extracts, DNA templates, protein kinase substrates, and to perform checkpoint assays. In addition, we describe related methods that provide useful readouts of the DNA damage response.