Relationship between thymineless death and ultraviolet inactivation in Escherichia coli.

Gallant, J. (Johns Hopkins University, Baltimore, Md.), and S. R. Suskind. Relationship between thymineless death and ultraviolet inactivation in Escherichia coli. J. Bacteriol. 82:187-194. 1961.-At 37 C, cultures of Escherichia coli strain B3 growing in the absence of thymine undergo unbalanced growth and thymineless death. Thymineless death also occurs at 37 C in 2 mug of chloramphenicol per ml despite virtually complete inhibition of cell growth and net protein synthesis. Thymineless cultures growing at 25 C exhibit unbalanced synthesis of ribonucleic acid and of protein without lethality. Examination of the kinetics of ultraviolet inactivation of cells grown under these three conditions indicates that the mean lethal dose of ultraviolet irradiation decreases with unbalanced protein synthesis whether or not thymineless death occurs, whereas the latter is specifically correlated with a transition from multihit to single hit inactivation kinetics. The time course of this transition correlates well with that of thymineless death, and preirradiated cells show a shorter lag period before the onset of thymineless death. These results, therefore, suggest that thymineless death is due to an inactivation of those cellular units which are sensitive to ultraviolet irradiation, presumably nuclei or some nuclear function.