Equal amounts of mutant LMW-PTP or BSA protein, or buffer alone (mock-attached) were coupled to beads and incubated with lysate from pervanadate-treated transfected amebae overexpressing epitope-tagged putative substrate proteins or control URE3-BP protein, with BSA, or with lysis buffer only. Samples were subjected to SDS-PAGE, and immunoblots probed with S tag antibody. Overexpresser lysates: A = 328.t00002 + C-term tag, B = Type A flavoprotein + C-term tag, C = Putative Ser/Thr kinase + N- and C-term tag, D = Putative Arp 2/3 complex 34 kDa subunit + N-term tag, E = 503.t00001 + N- and C-term tag, F = Ribose-phosphate pyrophosphokinase + N- and C-term tag, G = URE3-BP + N- and C-term tag. (A). Sample lysates alone (5 μg/lane) were immunoblotted to test for epitope-tagged protein expression. (B), (C), (D). Substrate-trapping mutant LMW-PTP (Mut), BSA (BSA), or mock-attached (Beads) Affi-Gel 15 beads were incubated as indicated with lysate from putative substrate overexpressers, control URE3-BP overexpressers, BSA in lysis buffer, or lysis buffer alone.