Fig. 1. Mutating serine 345 to alanine abolishes the change in Chk1 mobility in response to CPT and UV light and confers UV sensitivity. (A) CLUSTAL W alignment of the non-catalytic domains of human, fission yeast, frog and mouse Chk1. Numbers refer to amino acids in the fission yeast protein. (B) NW223 (Chk1), NW457 (T323A), NW444 (S345A) and NW481 (S367A) cells grown to mid-log phase were treated with CPT, lysed, subjected to SDS-PAGE and immunoblotted with 12CA5 anti-HA antibody. (C) Strains shown in B were grown to mid-log phase, spread on agar plates, treated with 100 J/m² UV light, lysed, subjected to SDS-PAGE, and immunoblotted with 12CA5 anti-HA antibody. (D) NW223 (chk1⁺), NW158 (chk1::ura4), NW457 (chk1T323A), NW444 (chk1S34A), and NW481 (chk1S36A) cells were grown to mid-log phase, resuspended to 1x10⁷ cells/ml, spotted onto agar plates, and incubated at 30°C for approximately 3 days.