highly significantp ≤ 0.001
p values were determined using a heteroscedastic, two-tailed t test and are indicated as single asterisk for p ≤ 0.05 (significant), double asterisk for p ≤ 0.01 (highly significant) and triple asterisk for p ≤ 0.001 (very highly significant). c As control for the functionality of NQO as UV-mimetic agent, HeLa cells were either treated with DMSO (−NQO) or 1 μM NQO (+NQO) for 3 h and subsequently analysed by immunostaining using specific antibodies for UBF and Nop58 for the presence of nucleolar caps.