Additional S1333 mutations alter ATR kinase activity.

<p>The indicated ATR mutant or wild type proteins complexed with ATRIP were purified and incubated with GST-MCM2 substrate, [γ-³²P]-ATP, and GST-TOPBP1-AAD (GST-AAD) or GST. Kinase reactions were separated by SDS-PAGE and [³²P]-MCM2 detected by autoradiography. Quantitation of the fold activation compared to wild type protein incubated with GST measured by a phosphorimager is indicated below each lane. The amount of ATR and MCM2 present was detected by Coomassie blue (CB) or immunoblotting (IB) as indicated. Each mutant was tested at least three times and a representative experiment is shown.