NUCLEIC ACID METABOLISM IN RELATION TO THE

It has been shown by Lwoff (1953) that the quantitative response of inducible lysogenic microorganisms to ultraviolet irradiation is a function of the physiological condition of the organisms at the time of the irradiation. If Bacillus megaterium is starved of its carbon source for several hours prior to the ultraviolet irradiation, it acquires an enhanced resistance to the irradiation. The number of surviving cells is increased; the number of infectious centers is decreased. The enhanced resistance, or inapti-tude, can be conferred upon lysogenic organisms by withholding their source of nitrogen, or of essential amino acids as well (Jacob, 1952; Borek, 1952). Since the understanding of a block to a bio-chemical reaction has often helped to elucidate the mechanism of the reaction itself, we have undertaken a study of inaptitude with the hope that such a study might contribute to our under-standing of induction-the ultraviolet irradiation induced proliferation of the otherwise latent phage. We have previously reported that the culture medium in which the lysogenic organisms had starved can partially protect well nourished organisms against the effects of ultraviolet irradiation (Borek and Rockenbach, 1952). We have traced this protection in part to a mechani-cal screening of the irradiation by ultraviolet absorbing substances present in the starvation medium. Chromatographic analysis of the medium in which the lysogenic organisms had starved revealed the presence of bases and of nucleotides as well. The excretion of nucleic aci