Abstract
The cell-cycle checkpoint monitors the progression of the cell cycle, detects a problem such as DNA damage, and arrests the cycle until the problem is solved. We previously identified the AtRAD26 gene being involved in the checkpoint in Arabidopsis. The AtRAD26-disrupted plant was sensitive to DNA damaging agents or cell-cycle inhibitors, which is reminiscent of the phenotype of AtATR-disrupted plant. The AtRAD26 protein contained two strokes of SQ sequences, potential target sites of PIKK including ATR and ATM.
To clarify whether the AtRAD26 is regulated by PIKK, we used the bacterially-expressed N-terminal region of AtRAD26 as a substrate for in vitro phosphorylation assay. It incorporated 32P when incubated with [γ-32P]ATP and the nuclear extract from wild-type plants. By contrast, the 32P-incorporation was reduced when incubated with the nuclear extract from AtATR-disrupted plants. This suggests that the AtRAD26 is phosphorylated by (a) checkpoint-related kinase(s) including AtATR.
