We previously identified the deubiquitylase USP9X as a G2/M-specific CDC14B interactor (PXD012732). The functional connection of these proteins has been further investigated by a quantitative comparison of USP9X phosphorylation in WT vs CDC14B-overexpressing HEK 293Tcells (ATCC® CRL-3216™). The approach identified USP9X serine 2563 as a specific CDC14B target. Phosphorylation at USP9XS2563 has been confirmed by in-house phosphospecific antibodies.