Figure 1.

Ser³⁰⁷ in IRS-1 mediates the inhibitory effect of anisomycin on insulin-induced tyrosyl phosphorylation of IRS-1. CHO cells were transiently transfected with plasmids (10 μg) encoding IRS-1 or IRS-1^S307A. Twenty-four hours later, cells were deprived of serum overnight and preincubated for 30 minutes with 5 μg/ml anisomycin before 50 nM insulin stimulation for an additional 5 minutes. (a) Proteins (30 μg) in cell lysates were resolved by SDS-PAGE and immunoblotted with anti-phosphotyrosine. (b) The same blot was reprobed with αIRS-1. The migration of molecular weight standards, IRS-1, and IR is indicated.