Figure 5

DSB repair kinetics in cells undergoing constitutive L1 expression. (A) Kinetics of 53BP1 foci formation induced by H₂O₂. After treatment with 7.8 mmol/l H₂O₂, nuclei of HeLa open reading frame (ORF)2 and HeLa ORF2 ER-- cells were stained with Hoechst and 53BP1 foci are revealed by immunofluorescence. These cells were fixed and stained at three time points (45, 75 and 135 minutes after H₂O₂ treatment). (B) Quantification of kinetics of 53BP1 foci formation induced by H₂O₂ 53BP1 foci from (A) were counted. Data are means and SD (error bars) of independent measurements. Asterisks signify a significant (Student t-test, P ≤ 0.05) difference from 53BP1 foci seen in HeLa ORF2 ER-- cells. (C) Kinetics of 53BP1 foci formation induced by transient L1 ORF2 expression. After transient transfection with a vector expressing L1 ORF2, nuclei of HeLa ORF2 and HeLa ORF2 ER-- cells were stained with Hoechst and 53BP1 foci are revealed by immunofluorescence. These cells were fixed and stained at three time points (16, 20 and 48 hours after transfection). (D) Kinetics of transient 53BP1 foci formation induced by transient L1 ORF2 expression. 53BP1 foci at 16, 20 and 48 hours after transfection were quantified in three separate experiments. Data are means and SD (error bars) of three independent measurements. Asterisks signify a statistically significant (Student t-test, P ≤ 0.055) difference from 53BP1 foci levels seen in HeLa ORF2 ER-- cells.