Enhanced repair of DNA interstrand crosslinks in S phase

Hela cells synchronized in G1 and S phases of the cell cycle were transfected with pEGFP crosslinked with trioxsalen. Twelve hours later the number of fluorescent cells was determined by fluorescent microscopy. Cells in S phase have repaired 0.2–0.3 ICL/kb over the 12 h period, while cells in G1 phase repaired interstrand crosslinks much more poorly. The crosslinked plasmids were efficiently recruited to the nuclear matrix both in G1 phase and S-phase, which showed that the poor repair of G1 cells was a result of a lack of DNA replication rather than of a lack of matrix attachment.