Figure 4. Focus formation of EGFP-Spartan is dependent on its PIP box and UBZ4 domain. (A) Focus formation of EGFP-Spartan in response to DNA damage. Wild-type or indicated mutants of Spartan were stably expressed as a fusion protein with EGFP in U2OS. Localization of EGFP-Spartan was visualized 3 h after UV (20 J/m2) or 6 h after HU (10 mM) treatment. (B) Quantitation of cells containing EGFP-Spartan Foci. Cells were treated as in (A), and percentage of cells containing more than ten EGFP-Spartan foci is presented as mean ± SD (n = 3).