Kim Eun Mi, Burke Daniel J
Department of Biochemistry and Molecular Genetics, University of Virginia Medical Center, Charlottesville, Virginia, United States of America.
PLoS Genet. 2008 Feb 29;4(2):e1000015. doi: 10.1371/journal.pgen.1000015.
The DNA damage checkpoint and the spindle assembly checkpoint (SAC) are two important regulatory mechanisms that respond to different lesions. The DNA damage checkpoint detects DNA damage, initiates protein kinase cascades, and inhibits the cell cycle. The SAC relies on kinetochore-dependent assembly of protein complexes to inhibit mitosis when chromosomes are detached from the spindle. The two checkpoints are thought to function independently. Here we show that yeast cells lacking the DNA damage checkpoint arrest prior to anaphase in response to low doses of the DNA damaging agent methyl methane sulfonate (MMS). The arrest requires the SAC proteins Mad1, Mad2, Mad3, Bub1, and Bub3 and works through Cdc20 and Pds1 but unlike the normal SAC, does not require a functional kinetochore. Mec1 (ATR) and Tel1 (ATM) are also required, independently of Chk1 and Rad53, suggesting that Mec1 and Tel1 inhibit anaphase in response to DNA damage by utilizing SAC proteins. Our results demonstrate cross-talk between the two checkpoints and suggest that assembling inhibitory complexes of SAC proteins at unattached kinetochores is not obligatory for their inhibitory activity. Furthermore, our results suggest that there are novel, important targets of ATM and ATR for cell cycle regulation.
DNA损伤检查点和纺锤体组装检查点（SAC）是两种对不同损伤作出反应的重要调节机制。DNA损伤检查点检测DNA损伤，启动蛋白激酶级联反应，并抑制细胞周期。SAC依赖于着丝粒依赖性的蛋白质复合物组装，在染色体与纺锤体分离时抑制有丝分裂。这两个检查点被认为是独立发挥作用的。在此我们表明，缺乏DNA损伤检查点的酵母细胞在受到低剂量DNA损伤剂甲磺酸甲酯（MMS）刺激时，会在后期之前停滞。这种停滞需要SAC蛋白Mad1、Mad2、Mad3、Bub1和Bub3，并通过Cdc20和Pds1起作用，但与正常的SAC不同，它不需要功能性着丝粒。Mec1（ATR）和Tel1（ATM）也同样需要，且不依赖于Chk1和Rad53，这表明Mec1和Tel1通过利用SAC蛋白来响应DNA损伤抑制后期。我们的结果证明了这两个检查点之间存在相互作用，并表明在未附着的着丝粒处组装SAC蛋白抑制复合物对于其抑制活性并非是必需的。此外，我们的结果表明，存在ATM和ATR用于细胞周期调控的新的重要靶点。
