| Abstract: | 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. |
