"Interaction of Siah2 with PHD3. ( a ) HEK293 cells were transfected in 60-mm cell culture plates for 2 days with the indicated expression plasmids. The cells were lysed, and the lysates were subjected to FLAG immunoprecipitation (IP), as described under "" Materials and Methods "". Aliquots of the cell lysates and immunoprecipitates were analyzed by western blotting with the anti-HA antibody. Both full length Siah2 and Siah2 SBD bind to PHD3 to the same extent. In the IP, the presence of the faint band in the empty vector lane is due to non-specific binding of PHD3. The same membrane was reblotted with FLAG antibody to detect FLAG tagged Siah2 proteins. ( b ) GST-Siah2 SBD pulldown of HA-PHD3. Cell lysate of HEK293 cells transfected with HA-PHD3 was incubated with GST-Siah2 SBD immobilized on GSH agarose beads and the reaction was performed as described under "" Material and Methods "". The empty expression vector alone was expressed as a GST control for non-specific binding of HA PHD3. After the incubation, the lysate was removed, the GSH-agarose beads were washed, and bound HA-PHD3 was analyzed by Western blotting using anti HA antibody. The pull down assay confirmed the interaction of Siah2 SBD with PHD3."