Ufd4p, the E3 of the UFD pathway, is physically associated with the
proteasome. (A) Ufd4p interacts with Rpt6p in the
GST-pulldown assay. Extracts of S. cerevisiae containing
overexpressed HA-Ufd4p were incubated with glutathione-agarose beads
preloaded with different GST fusions, as indicated. The retained
proteins were eluted, fractionated by SDS/8% PAGE, and
immunoblotted with anti-HA antibody. Approximately equal amounts of
different GST fusions were immobilized on glutathione-agarose beads in
these assays, as verified by Coomassie staining (data not
shown). (B) In vivo association of Ufd4p
and Rpt6p. Extracts of S. cerevisiae JD52
(UBR1) expressing both HA-Ufd4p and Rpt6p-FLAG, HA-Ufd4p
alone, or Rpt6p-FLAG alone were incubated with anti-HA antibody. The
immunoprecipitated proteins were separated by SDS/10% PAGE and
transferred to nitrocellulose membrane. (Upper) The
results of immunoblotting with anti-HA antibody. (Lower)
The data with anti-FLAG antibody. (C)
Coimmunoprecipitation of Rpn1p and Ufd4p. Extracts of S.
cerevisiae JD52 expressing both HA-Ufd4p and Rpn1p-FLAG,
HA-Ufd4p alone, or Rpn1p-FLAG alone were incubated with anti-HA
antibody, followed by the immunoprecipitation/immunoblotting
procedure described in B, except that SDS/7%
PAGE was used.