Evidence for the direct action of colicin K on aerobic 32P/sub i/ uptake in Escherichia coli in vivo and in vitro

Pentachlorophenol (PCP)-sensitive incorporation of 32 P-labeled orthophosphate ( 32 P i ) into nucleotides and nucleic acids by disrupted spheroplasts of Escherichia coli was inhibited by addition of colicin K. Incorporation by intact cells was also inhibited by a similar concentration of colicin K. Various colicin K-resistant mutants were isolated, and their ability to incorporate 32 P i was tested. When T6 r - colK r mutants (T6 phage-resistant) and tol I mutants (T6-sensitive, colicin E-sensitive) were converted to disrupted spheroplasts, their 32 P i -incorporation became sensitive to colicin K. On the contrary, incorporation by disrupted spheroplasts from tol II mutants (T6-sensitive, colicin E-resistant) was fairly resistant to colicin K like that of intact cells. A modification of the cell surface of T6 r - colK r mutants, caused by mutation to novobiocin-permeable, T4 phage-resistant cells, restored the sensitivity of the cells to colicin K. The modified T6 r - colK r cells did not adsorb T6 phage or colicin K, indicating that the receptors for T6 phage or colicin K are not reactivated by this modification. Similar treatment of tol I mutants did not have this effect. These observations strongly suggest that colicin K can act on its target on the cell membrane if it can penetrate the cell surface to reach this target. The receptor for colicin K on the cell surface, which may be part of the T6 phage-receptor, may have some unknown function in relation to the action of colicin K in normal cells, but tends to become dispensable if the cells become permeable to colicin K.