Colicin M of Escherichia coli C1139 was isolated in pure form. It consisted of a single polypeptide with a molecular weight of 27,000 ± 2,000. Colicin M lysed sensitive cells of E. coli but had to act continuously up to the point when lysis commenced (after 20 min). Colicin M was largely resistant to hydrolysis by trypsin except when adsorbed to cells. Within 4 to 5 min after addition of colicin M, cells could be rescued by trypsin or sodium dodecyl sulfate. Later, colicin M was apparently inaccessible to these inactivating agents. Killing of cells by colicin M required Ca2+ ions. Cells could be rescued with ethylene glycol-bis(f-aminoethyl ether)-N,N'-tetraacetate (EGTA) immediately before the onset of lysis. Under these conditions, colicin M remained bound to the cells, and it became again sensitive to trypsin. We conclude that under the influence of EGTA colicin M is removed from its site of action and becomes again accessible to trypsin at the cell surface. Colicin M was originally defined on the basis that resistant cells were cross-resistant to phages Ti and T5 (6). Later it was shown that colicin M causes lysis of sensitive cells (2). Both observations were of interest since the uptake of the toxic protein required the function coded by the

The structure of colicin M of Escherichia coli was studied with regard to its organization into functional domains. A proteolytic fragment with an Mr of 24,000 was isolated which comprised the carboxyterminal portion of the protein. It adsorbed to the outer membrane receptor protein and inhibited killing of cells by colicin M and by phage T5 that uses the same receptor. The fragment killed cells when the outer membrane was rendered permeable to macromolecules for a short time by the osmotic shock procedure. It is concluded that the fragment contains the receptor binding site and the active center but is lacking the sequence required for transport into cells. The carboxy-terminal amino acid sequence-Lys-Arg of the fragment was identical to that obtained from colicin M. Release of lysine and arginine led to inactivation of colicin M. The sequence of the first 39 amino acids of the amino terminal end of colicin M was determined.

A mutant of Bacillus subtilis synthesizes a variety of c-alicyclic fatty acids when fed with the respective alicyclic carboxylic acids. These fatty acids are: wcyclopropane, c-cyclobutane, co-cyclopentane, o.)-cyclohexane, and co-cyclohexene fatty acids. These unusual fatty acids did not lead to an inhibition of growth at

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