Modes of action of colicins E4-E7: rates of basic biosyntheses inhibition.

The progress of the inhibition of prominent biopolymer syntheses (namely of DNA, RNA and protein synthesis) in cultures of susceptible bacteria Escherichia coli treated with colicins E4, E5, E6 or E7 was followed. The method used was the measurement of incorporation of specific radioactive precursors into an instantly precipitable fraction. All the three syntheses being inhibited successively, progressively and with different urgency during unfolding of the lethal effect of each colicin, emphasis was put on a comparative mathematical analysis of the development of the biosyntheses inhibition rates. In bacteria treated with colicins E4, E5 or E6, protein synthesis was blocked preferentially and most heavily, followed by cessation of DNA synthesis and finally also by a rather slowly proceeding impairment of RNA synthesis. (In E6-treated cells, damage to DNA synthesis started prior to that to protein synthesis.) Thus, the effect of colicins E4, E5 and E6 follows the general pattern of colicin E3 action. Bacteria treated with colicin E7 developed an immediate block of DNA synthesis, soon followed by protein and (again after a significant delay) by RNA synthesis switch-off. Thus the action of colicin E7 is closely related to that of colicin E2. The presumptive direct targets of these colicins remain to be elucidated.