Figure 1.

CSN1 is phosphorylated by ATM at Ser-474 in response to UV irradiation. Cells were irradiated with UV at 25 J/m² and incubated in fresh media, with or without the ATM inhibitor Ku 55933 as indicated. (a) Western blotting showing ATM auto-phosphorylation; (b) the CSN1 component of CSN is phosphorylated by ATM. CSN was purified using the Flag tag on the eCSN5 subunit, and analyzed by western blotting; eCSN5 was used as a loading control. (c) Mutation of S474 abolishes CSN1 phosphorylation. Western blot analysis of affinity purified CSN1 from cells expressing wt CSN1 or S474A CSN1 mutant as indicated. Anti-ATM-pS1981 antibodies were used on all panels.