Updated FTP location. FT293 cells which express FLAG-tagged CLPX, in which deleted endogenous CLPX were used for the study. FT 293 cells which express a chimeric protein composed of the mitochondrial transit peptide region of ornithine transcarbamylase and Flag-tagged luciferase were used as control. Each of FLAG-tagged proteins were expressed by doxycycline-inducible manner. The FLAG-tagged proteins were immunoprecipitated using anti-DDDK-tag antibody-conjugated agarose beads, and the immunoprecipitated proteins were eluted from the agarose beads by DDDDK peptides. The eluted precipitates were digested with trypsin.