Figure 3.

Atm-dependent and -independent phosphorylation of Smc1 on Ser 957 and Ser 966 in vivo. (A) Immunoblots probing 50 ng of phosphorylated or unphosphorylated synthetic peptides using rabbit polyclonal antibodies raised against peptides containing Ser 957-p or Ser 966-p. (B) Immunoblot analyses using the two phosphoserine-specific antibodies (top and middle) or an anti-SMC1 antibody (K1; bottom) on SMC1 protein from normal (WT; GM0637) or A-T (GM9607) fibroblasts treated with ionizing irradiation (IR; 10 Gy, 2 h), ultraviolet light (UV; 50 Jm⁻², 2 h) or hydroxyurea (HU; 1 mM, 24 h). The arrow (middle) points to the band specifically recognized by the anti-phosphoserine 966 antibody (note a nonspecific band runs just below the S966-p band).