Photodynamic action of proflavine on coliphage T3. 3. Damages to the deoxyribonucleic acid associated with Rxl and Rx2.

Ultracentrifugational studies with deoxyribonucleic acid (DNA) extracted from phage exposed to light in the presence of either 0.25 or 8.5 mug of proflavine per ml reveal that the lethal damage of Rx1 renders DNA alkali-labile, with lethality resulting from damage that occurs singly on either strand or simultaneously on both strands. Apparently nonlethal damages temporally associated with Rx1 consist of (i) heat and alkali-labile cross-links (which produce undenatured DNA that migrates at 45S) and (ii) heat-labile bonds. The formation of 45S material is a linear function of light dose, and the production of this material ceases when Rx2 appears at the higher dye concentration. No tendency to plateau is seen at 0.25 mug of dye per ml. The nature of the lethal damage of Rx2 could not be determined. Damages that were temporally associated with Rx2 at 8.5 mug of dye per ml were heat-labile, alkali-stable cross-links (undenatured DNA, 38 to 41S; alkali-denatured-reneutralized DNA, 85 to 89S) and some double-stranded breaks. No such changes were seen at 0.25 mug of dye per ml.