Photobiology of Rna Bacteriophages—i. Ultraviolet Inactivation and Photoreactivation Studies*

Biologically active f2‐RNA, Obtained from bacteriophage f2, was inactivated by ultraviolet (u.v) light (2537 Å) with a quantum yield of 3.3 ± 0.3 times 10 ‐3 when assayed in the dark with protoplasts of an F‐ strain of E. coli k12. Assay under “black light” gave a quantum yield of 2.7 ± 0.5 times 10 ‐3 which was just enough lower to suggest that 17 per cent photorecovery of the u.v. lesions has taken place. Intact phage f2 was inactivated by u.v. radiation with a quantum yield of 0.7 ± 0.12 times 10 ‐3 , Thus the whole phage is much less sensitive than the free RNA. No evidence of photorecovery was found in u.v.‐irradiated RNA phage 7S assayed in its host Pseudomonas aeruginosa .