Figure 2.

recF and recR cells show a delay in the recovery of DNA synthesis after UV irradiation. (A) Cells were prelabeled with [³H]thymine. At time 0, half the culture was removed and given a dose of 25 J/m² (•), while the other half was left unirradiated (□). The relative increase of DNA as measured by ³H incorporation is plotted. (B) The amount of replication occurring within 1 h postirradiation was analyzed by alkaline CsCl density gradients. Cells prelabeled with [¹⁴C]thymine were irradiated or not at time 0. Cells then were filtered and grown in media containing 5-bromodeoxyuridine and [³H]thymine for 1 h to density label replication occurring after time 0. □, ¹⁴C prelabeled DNA; ○, ³H replicated DNA in unirradiated cultures; and •, ³H replicated DNA in irradiated cultures.