POTENTIAL MECHANISMS OF PHOTODYNAMIC INACTIVATION OF VIRUS BY METHYLENE-BLUE - I - RNA-PROTEIN CROSS-LINKS AND OTHER OXIDATIVE LESIONS IN BACTERIOPHAGE-Q-BETA

A spectrum of oxidative lesions was observed in a bacteriophage-based model system that is very sensiaire to the photodynamic activity of se lected 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 w ith the formation of several specific lesions: (1) carbonyl moieties o n proteins, (2) 8-oxo-7,8-dihydroguanine (8-oxoGua), and (3) single-st rand breaks (ssb) in the RNA genome and (4) RNA-protein crosslinks. Fo rmation 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 co ncentrations but appeared nea. to be significant at the lower concentr ations 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 num ber 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 suspens ions. A significant increase over background of RNA-protein complexes (including full-length Q beta RNA) was observed at the fewest concentr ation of MB tested (0.5 mu M), which corresponded roughly to an averag e of 2 lethal hits: per phage or approximately 13% survival compared t o the zero MB control (100% survival). Due to its close correlation wi th Q beta inactivation and its expected lethality, RNA-protein crossli nk formation may be important as an inactivating lesion in bacteriopha ge Q beta following MB+L exposure.