Polyamine content of nucleated and enucleated Escherichia coli cells.

There is currently considerable interest in the physiological function(s) of polyamines. Investigations have shown many in vitro interactions of polyamines with various cellular components, particularly deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and ribosomes; the in vivo role(s) of polyamines is still unclear (H. Tabor and C. W. Tabor, Pharmacol. Rev. 16:245, 1964). This is owing largely to the uncertainty concerning the in vivo distribution of polyamines within the cell. Extrapolation of in vitro binding studies of the polyamines to subcellular components to in vivo localization of the polyamines is complicated by the redistribution of these highly basic substances after cell disintegration. Recently, Adler et al. (Proc. Natl. Acad. Sci. U.S. 57:321, 1967) reported the isolation of a strain of Escherichia coli (K-12 P678-54) which produces miniature DNA-deficient cells designated "minicells." This unique property of this strain of E. coli provides a system to test whether there exists a pronounced preferential binding of the polyamines, or of a particular polyamine, to the DNA. If such were the case, one might expect the minicells to contain relatively less polyamines. We therefore examined the amounts of DNA, RNA, and polyamines of E. coli K-12 P678-54 and its minicells and have found no evidence for preferential binding of the polyamines to DNA. Growth of the organism (kindly provided to us by Dr. Adler) and the separation of the minicells from normal cells were carried out as described by Adler et al. (Proc. Natl. Acad. Sci. U.S. 57: 321, 1967). DNA, RNA, and polyamines were determined by standard methods (K. Burton, Biochem. J. 62:315, 1956; W. Medbaum, Z. Physiol. Chem. 258:117, 1939; K. Kim, J. Bacteriol. 91:193, 1966; D. T. Dubin and S. M. Rosenthal, J. Biol. Chem. 235:776, 1960). The polyamines were also subjected to thin-layer chromatography on silica gel with two solvent systems (methanol-concentrated NHs, 7:3, v/v, and methanol-concentrated HCI, 8:2, v/v), which further identified the polyamines and eliminated the possibility of ornithine or lysine contaminating the putrescine obtained from column chromatography. The DNA, RNA, and polyamine contents of the minicells and of normal K-12 P678-54 cells are shown in Table 1. In the normal cells, the polyamines, assuming two positive charges per putrescine and three positive charges per spermidine, can neutralize a total of 12 to 13% of the phosphate groups in the nucleic acids. If the DNA, which is approximately 8 to 9% of the total nucleic acids, were to show a preferential binding