Antibodies used in this study are as follows. Anti-human Claspin, anti-mouse Claspin, anti-MCM4, and anti-MCM4 S6T7 were previously described.19 (link) Anti-LaminB (sc-6216), anti-Chk1 (sc-8408), anti-p53 (sc-99), anti-Claspin (sc-376773) and anti-MCM2 (sc-9839) were from Santa Cruz Biotechnology; anti-Flag (M185-3L) were from MBL; anti-Chk1 S345(#2341 or #2348), anti-Chk1 S317 (#2344), anti-mTor (#2983), anti-mTOR S2448 (#5536), anti-p44/42 MAPK (Erk1/2) (#4695), anti- SAPK/JNK (#9252), p38 MAPK (#8690), anti-p38 MAPK T180/Y182 (#4511), anti-p44/42 MAPK (Erk1/2) T202/Y204 (#4370), anti-SAPK/JNK T183/Y185 (#4668), anti-PDK1 (#3062), anti-PDK1 S241 (#3438), anti-PI3 kinase p110β (#3011), anti-PI3 kinase p110γ (#5405), anti-PI3 kinase p110α (#4249), anti-PI3 kinase class III (#3358), anti- p70 S6 kinase T389 (#9234), anti-p70 S6 kinase (#9202), anti-4E-BP1 T37/T46 (#2855), anti-4E-BP1 (#9644), anti-Caspase-3 (#14220), anti-Akt S473(#4058) and anti-Akt (#4691) were from Cell signaling; anti-tubulin (T5168) was from Sigma-Aldrich; anti-MCM2 S53(A300-756A) was from Bethyl; anti-p53 S37 (PAB12641) was from Abnova; anti-histone H2A.X Ser139 (05-636) and anti-histone H3 Ser10 (05-598) were from Merck Millipore; anti-Rb (GTX50459) was from GeneTex.