CONSTANCY OF THE UV SENSITIVITY OF E. COLI DURING THE CELL CYCLE*

Abstract— Cells from slowly growing glucose-limited chemostat cultures of two different strains of Escherichia coli were separated by size on sucrose gradients, and 254-nm ultraviolet (UV) survival curves were obtained for samples of the different cell sizes. With the repair-deficient strain B_s-1 there was no observable change in survival curve during the cell cycle. With the repair-proficient strain 15 THU, there was no observable change in the final slope, but y -axis intercepts increased slightly for the older cells. Our results provide further evidence for the approximate independence of UV sensitivity, k , upon cell age within the division cycle and upon the presence or absence of DNA synthesis. They are consistent with a model in which UV lesions in newly replicated strands of DNA do not contribute to lethality.