Studies of the inactivation of viruses by ionizing radiations (i.e. X-rays and the radiations

Three bacteriophages (S-13, C-36 and S taph-K ) were irrad ia ted by y-rays, X -rays and a-rays. The survival curves were exponential, and the effect of a given dose was independent of the exposure tim e. F or any given phage the inactivation doses of the three radiations increased in the order y-rays, X -rays, a-rays, while for any given rad iation the inactivation doses of the three phages dim inished in the order S-13, C-36, S taph-K , which is the order of in ­ creasing size. These observations lead to the conclusion th a t a single ionization suffices to inactivate a phage particle. In the case of the sm allest phage investigated (S-13) th is ionization is effective w herever in the particle it is produced, and reasons are given for concluding from th is fact th a t S-13 is a m acrom olecular type of virus analogous to the erystallizable p lan t viruses. In the case of the larger phages (C-36 and Staph-K ), while a single ionization can in ­ ac tiva te a phage particle it is no t sufficient for it to be produced anyw here in the phage partic le ; to be effective it m ust be produced in a more restric ted region. I t is suggested th a t th is radiosensitive region constitu tes the genetical m ateria l of the phage, and on the basis of th is differentiation into genetic and non-genetic m ateria l these phages are regarded as p rim itive single-celled organism s ra th e r th an macromolecules.