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A group of nitrogen-containing steroids closely related in structure was screened for antibacterial activity, by use of Bacillus subtilisand Sarcina luteaas the test organisms. The most active compounds were cholesterol derivatives containing a tertiary or quaternary nitrogen in, or attached to, the A ring. Similar methyltestosterone or progesterone derivatives were inactive. All of the cholesterol derivatives that inhibited growth were surfactant, and, structurally, they would be classified as cationic detergents. Some of the inactive compounds were surfactant, but, structurally, they would be classified as nonionic detergents. Certain features of the antibacterial activity of one of the active steroids—ND 212 (4-dimethylaminoethyl-4-aza-5-cholesten-3-one methiodide)—were studied. Growth of a culture of B. subtiliscontaining 5 × 107cells per milliliter was inhibited by 1 μg/ml (1.7 × 10−6m) of ND 212. The amount of growth inhibition was directly related to both cell and steroid concentration. Loss of viability was rapid and irreversible. With B. subtilis, cell lysis was observed. With S. luteagrown in C14-glucose, ND 212 caused release into the media of up to 25% of the cellular radioactivity. Extensive leakage occurred before loss of viability was observed. At bacteriostatic azasteroid concentrations, there was little leakage. ND 212 was readily bound in large amounts to B. subtiliscells. Inactive azasteroids were bound poorly. C14-cholestanone was also bound, whereas C14-methyltestosterone and C14-progesterone were not bound in significant amounts. At least 50% of the bound C14-cholestanone was associated with the membrane fraction.

The distribution of ribosomes, 30 and 50Ssubunits and polysomes, at three different growth rates of Escherichia colistrains B and K-12 has been studied. The usual percentage of subunits is about 20%. However, at the lowest growth rate (μ = generations/hour), μ = 0.45 at 30C, the proportion of subunits is about 30%. An exceptional situation exists in K-12 strains growing at maximum growth rate, μ = 1.35, where the percentage of subunits is 45%. Several points of control over ribosome production are thus indicated. It is suggested that “subunit pool” is essentially a reserve. Furthermore, the polysome content when related to deoxyribonucleic acid content varies directly with the growth rate, which indicates the average efficiency of polysomes in protein synthesis does not vary over the range of growth rates tested.

Escherichia colispheroplasts lysed by Brij 58 and deoxycholate were separated into supernatant (S) and membrane fractions by low-speed centrifugation. The membrane fraction was further divided into that which was releasable by deoxyribonuclease (fraction D) and that which was not (M). In the presence of 10−2mMg2+, the S, D, and M fractions contained, respectively, 60, 20, and 20% of the total cellular ribonucleic acid (RNA). Ribosomal and transfer RNA (rRNA, tRNA) were found in each fraction. The M + D fraction RNA was labeled more by a pulse label. Incorporation of uracil into the D fraction continued only as long as the uptake of exogenous uracil, suggesting that this was a major primary site of RNA synthesis. From pulse-labeled cells, each fraction contained precursor rRNA, and there was a 10SRNA in the M fraction. Ninety per cent of the ribosomal subunits and the ribosomal precursor particles, 26 and 43S, were in the S fraction. Precursor RNA (17S) was found in the 26Sprecursor particles. The D fraction contained 38% of the polysomes (this does not consider polysomes, if any, of the M fraction) which were labeled four times as much as the supernatant polysomes by a 1-min pulse of uracil. These results are interpreted to mean that new RNA is associated with a cytoplasmic membrane-RNA polymerase-DNA complex.

THE numerous 70S ribosomes found in bacterial extracts are believed to arise from the degradation of polysomes during preparation of the extracts. But do 70S ribosomes exist at all in vivo and, if so, to what extent ? Mangiarotti and Schlessinger1reported that in extracts of fragile mutants of E. coli 70S ribosomes always comprised less than 2 per cent of the total ribosome population. Kohler, Ron and Davis2, however, have shown that the amount of 70S ribosomes in Mangiarotti and Schlessinger's preparations was artefactually low.