CHAPTER 12 



Photoreactivation 



Renato Dulbecco 



Kerckhoff Laboratories of Biology, California Institute of Technology 



Pasadena, California 



Introduction. Historical note. Photoreactivation in bacteriophages: Conditions of 

 inactivation — Methods for studying photoreactivation — Adsorption of phage on bacteria 

 a necessary prerequisite for photoreactivation — Comparison of survival curves after 

 ultraviolet treatment in presence and in absence of photoreactivation — Kinetics of photo- 

 reactivation in phage T2 in condition of single infection — Kinetics of photoreactivation 

 of phage T3 — Kinetics of photoreactivation of phage T2 in condition of multiple infec- 

 tion — Action spectrum of the photoreactivating light — Action of chemical substances on 

 photoreactivation — Photoreactivation of bacteriophages inactivated by agents other than 

 ultraviolet — Photoreactivation of the induction process of phage carried lysogenically. 

 Photoreactivation of plant viruses. Photoreactivation of bacteria: Conditions under ivhich 

 'photoreactivation occurs — Effect of the growth stage of bacteria on photoreactivation— 

 Comparison of survival curves after ultraviolet treatment in presence and absence of photo- 

 reactivation — Kinetics — Action spectrum of the photoreactivating light — Chemical actions 

 connected with photoreactivation — Action of photoreactivation on the induction of mutation 

 by ultraviolet in bacteria. Photoreactivation in Streptomyces and fungi. Photoreactiva- 

 tion in yea-^t. Photoreactivation in protozoa. Photoreactii>ation in echinoderm zygotes 

 and gametes. Photoreactivation in salamander larvae. Photoreactivation in higher 

 plants. Conclusions and summary. References. 



1. INTRODUCTION 



The term "photoreactivation" designates the phenomenon in which 

 changes produced in different types of organisms, mainly microorganisms, 

 by ultraviolet radiation of wave lengths around 2500 A can be counter- 

 acted if the irradiated organisms, under proper conditions, are exposed to a 

 radiation of longer wave length, in the range between 3300 and 4800 A. 

 The phenomenon received its designation from the fact that it was first 

 n(3ted as a reversal of the inactivation produced by the ultraviolet radiation 

 in some microorganisms (fungi, yeasts, bacteria, bacteriophages) ; how- 

 ever, it includes reversal of effects of ultraviolet radiation other than inac- 

 tivation, such as mutation, delay in time of onset of division in echinoderm 

 eggs and in protozoa, decreased vigor in protozoa, and even morphological 

 changes. 



Since the outstanding feature of photoreactivation in microorganisms 



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