Figure 1.

Induction of tyrosine phosphorylation resulting from expression of PTP1B mutants in COS cells. Samples (50 μg) of protein from lysates of COS cells transfected with pMT2 alone (vector) or with pMT2 plasmids expressing wild-type PTP1B, PTP1B with a C215A mutation (M1), PTP1B with a D181A mutation (M2), or GST fusions of each of these proteins were immunoblotted with anti-phosphotyrosine mAb 4G10. Proteins showing substantial increases in their phosphotyrosine content are marked with the dark arrows on the left. The positions of the molecular mass markers (Sigma) myosin, β-galactosidase, phosphorylase, bovine serum albumin, ovalbumin, and carbonic anhydrase are marked on the right with thin arrows.