A spectrum of oxidative lesions was observed in a bacteriophage- based model system that is very sensitive to the photodynamic activity of selected dyes. When suspensions of the intact bacteriophage Q \beta were exposed to methylene blue plus light (MB+L), inactivating events, or "hits" occurred that were oxygen- dependent and that were associated with the formation of several specific lesions: (1) carbonyl moieties on proteins, (2) 8-oxo- 7,8-dihydroguanine (8-oxoGua), and (3) single-strand breaks (ssb) in the RNA genome and (4) RNA-protein crosslinks. Formation of carbonyl groups associated with protein in the Q \beta phage preparation correlated positively with photoinactivation of the phage with increasing doses of either of the sensitizers MB or rose bengal. Strand breaks in the Q \beta genomic RNA were observable at high MB concentrations but appeared not to be significant at the lower concentrations of MB, as full-length Q \beta RNA was observable well beyond the 99% inactivation point in MB dosage. It was shown that the number of 8-oxoGua lesions were unlikely to be sufficient to account for the number of lethal events. Following exposure to MB+L, crosslink formation between Q \beta RNA and protein was observed by virtue of the location of RNA at the interface of phenol-aqueous extractions of phage suspensions. A significant increase over background of RNA- protein complexes (including full-length Q \beta RNA) was observed at the lowest concentration of MB tested (0.5 mM), which corresponded roughly to an average of 2 lethal hits per phage or approximately 13% survival compared to the zero MB control (100% survival). Due to its close correlation with Q \beta inactivation and its expected lethality, RNA-protein crosslink formation may be important as an inactivating lesion in bacteriophage Q \beta following MB+L exposure.
J. E. Schneider, Jr., T. Tabatabaie, R. H. S. L. Maidt, X. Nguyen, Q. Pye, R. A. Floyd, "Potential Mechanisms of Photodynamic Inactivation of Virus by Methylene Blue I. RNA- Protein Crosslinks and Other Oxidative Lesions in Q \beta Bacteriophage," Photochem Photobiol,67, 350 (98).