Multiplicity reactivation and radiation stability

Abstract

Evidence is presented that the resistance to inactivation by P/sup 32/ decay of T4 bacteriophage-bacterium complexes, previously noted by Pratt, et al., ibid., 3: 409(1961), can be explained by the multiplicity reaction (MR) occurring between newly synthesized phage genomes. Intracellular synthesis of phage DNA commences about 5 min after injection in complexes of the phage T2 and T4; consequently a given dose of irradiation applied to the complexes at any time during this period will produce a eonstant amount of genetic damage (i.e., damage which prevents the phage DNA from acting as a pattern for the synthesis of new undamaged phage D A). However, since certain biochemical steps leading oward phage synthesis will have been completed during t is time, irradiation will cause a decreasing amount of functional damage. The complexes should therefore exhibit an increase in radiation resistanrce before the onset of DNA synthesis if some, at least, of the radiation-induced damage affected critical functions without of necessity causing irreparable genetic damage, in one of 2 ways: (a) the irradiation could produce some damage which was inherently only functional, or (b) a mechanism existed more » by which genetic damage was repaired or bypassed provided that the critical cistrons were intact. P/sup 32/ decay causes no damage which is only functional in nature, so that the 1st possibility cannot explain the results of Pratt, et al. The phenomenon of MR, which is observed when multicomplexes rather than monocomplexes are irradiated, represents an example of the 2nd possibility. It is suggested that multicomplexes, but not monocomplexes, should show an increase in radiation resistance before the onset of DNA synthesis. This prediction was verifled by comparing, during the early part of the latent period, the resistance to irradiation by ultraviolet light of monocomplexes and multicomplexes of phage T4. The multicomplexes began to show an increase in radiation resistance about 2 min earlier than the monocomplexes. The interpretation suggested for the experiments of Pratt, et al., reresupposes that in multicomplexes efficient MR can occur between damaged parental genonres during the early part of the latent period. It must therefore be assumed that the physiological condition of the host bacteria must alter during the first minutes of the latent period in such a way that they can support the reactivation process. It may well be that this alteration is intimately related to the completion of the early essential biosynthetic steps in phage synthesis. (H.H.D.) « less