Polyubiquitination of mammalian E2-C by the APC/C.
(A) Recombinant Myc-tagged cyclin B was subjected to an in vitro
ubiquitination assay by incubation with rabbit E1, bovine ubiquitin,
and either immunopurified human APC/C (hAPC/C) or recombinant mE2-C, as
indicated. The reaction mixtures were subjected to immunoprecipitation
with anti-Myc, and the resulting precipitates were subjected to
immunoblot analysis with antiubiquitin (upper panel) or
anti-cyclin B (lower panel). Cyc B, cyclin B. (B) Recombinant mE2-C was
subjected to in vitro ubiquitination assay, as in (A), in the absence
or presence of purified human APC/C. The reaction mixtures were
subjected to immunoprecipitation with anti-mE2-C, and the resulting
precipitates were subjected to immunoblot analysis with
antiubiquitin (upper panel) or anti-mE2-C (lower panel). (C)
Recombinant wild-type (wt) or mutant (C114S) mE2-C was subjected to in
vitro ubiquitination assay in the presence of purified human APC/C and
was processed as in (B). (D) Recombinant GST fusion protein of mutant
(C114S) mE2-C was subjected to in vitro ubiquitination assay in the
absence or presence of wild-type mE2-C, together with purified human
APC/C and processed as in (B).