Effect of 5-fluorouracil posttreatment on sensitivity to ultraviolet radiation and course of messenger RNA synthesis inEscherichia coli cells

The effect of 5-FU posttreatment and uracil starvation on sensitivity to ultraviolet radiation and on the course of messenger RNA synthesis was studied in the strainsEscherichia coli 15 T-U-his-,Escherichia coli BU- andEscherichia coli Br. 5-FU posttreatment in liquid medium increased the number of surviving cells, while posttreatment in uracil medium either did not affect resistance or lowered it. A correlation was sought between increased resistance and messenger RNA synthesis (or stabilization). Messenger RNA synthesis was studied by means of pulse-labelling with radioactive precursor and the amount of m-RNA was determined by measuring total RNA proteosynthetic activity. It was found that the amount of RNA with messenger activity increased in cells treated with 5-FU, but that it decreased during cultivation in uracil medium. It is assumed that the 5-FU-induced increase in resistance is based on the preferential promotion of repair processes under conditions of a reduced turnover and the consequent stabilization of the m-RNA molecules. The possible mechanism of this promotion is discussed.