A NUCLEAR MEMBRANE CHANGE AFTER PARTIAL HEPATECTOMY

Partial hepatectomy (67 per cent extirpation) of the rat leads to a change in the membrane of liver nuclei (purified with citric acid) detectable as an increase in electrophoretic mobility. No change is detectable 2 hours after the operation, but between 2 and 6 hours about a 1.4-fold increase in mobility occurs after which the mobility becomes constant at the elevated level. Removal of only 10 per cent of the liver causes no detectable change in 6 hours. Bilateral adrenalectomy immediately before partial hepatectomy does not affect the development of the nuclear change. Actinomycin D and p-fluorophenylalanine, but not noradrenalin, ionizing radiation, or EDTA, suppress the increase in electrophoretic mobility. The level of actinomycin D required to block the nuclear membrane change is 6 times greater than that necessary to prevent the rate increase in hepatic RNA metabolism that follows removal of part of the liver. This discrepancy and the difference in the response to noradrenalin indicate that, at least initially, the nuclear membrane change and the change in the rate of RNA synthesis are independent processes. The inability of EDTA to block the nuclear membrane change shows that the Zn⁺⁺ requirement for DNA replication is not related to the events that lead to the alteration in the electrokinetic properties of liver nuclei.

MECHANISM OF RESISTANCE TO ACTINOMYCIN IN BACILLUS SUBTILIS

Polsinelli, M. (University of Pavia, Pavia, Italy), O. Ciferri, G. Cassani, and A. Albertini. Mechanism of resistance to actinomycin in Bacillus subtilis. J. Bacteriol. 88:1567-1572. 1964.-Strains of Bacillus subtilis were rendered resistant to actinomycin D by serial transfer in increasing concentrations of the drug. Resistance to the antibiotic appeared to be due to an altered cell-wall permeability, because the resistant strains did not take up actinomycin. No evidence was found for the presence of an enzyme(s) degrading actinomycin. Deoxyribonucleic acid (DNA) extracted from the actinomycin-resistant strains was found to bind actinomycin to the same extent as the DNA extracted from susceptible strains. The genetic nature of the resistance to actinomycin was demonstrated by means of transformation. Resistant strains appeared to have almost completely lost their transformability, as well as the tendency to autolyze.

SKIN TUMORIGENESIS BY 7,12-DIMETHYLBENZ(A)ANTHRACENE: INHIBITION BY ACTINOMYCIN D

Topical application of actinomycin D during a short period of time immediately before and after a single application of 7, 12-dimethyl-benz (a)anthracene markedly inhibits subsequent tumor formation. The results indicate that the initial events of carcinogenesis are dependent on DNA-dependent RNA synthesis.

STUDIES ON ANTIBODY PRODUCTION. XII. INHIBITION OF PRIMING BY DRUGS

The effect of drugs upon the primary and the secondary antibody response to diphtheria toxoid in mice was studied using an experimental system previously described. Triethylenethiophosphoramide (thio-TEPA), chloramphenicol, 6-mercaptopurine, 8-azaguanine, and versenate were found to inhibit, partially or completely,"priming" for the secondary response. Thio-TEPA, chloramphenicol, and 6-mercaptopurine, in doses exceeding those effective in inhibiting priming, did not cause alteration of the secondary response when given only during the secondary response. However, when chloramphenicol and amethopterin were given for 5 days prior to and at least 5 days after the second antigen injection, slight suppression of peak secondary titers occurred. Therefore, drug dosages effective in suppressing priming had less effect on the secondary response. It thus appears that there is a real difference between "priming" and the induction of antibody synthesis.

EFFECTS OF POLYCYCLIC AROMATIC CARCINOGENS ON VIRAL REPLICATION: SIMILARITY TO ACTINOMYCIN D

When incorporated into a nutrient overlay, the carcinogenic hydrocarbons benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene inhibit plaque formation by herpes virus and vaccinia virus, DNA viruses, but not by Sindbis virus, an RNA virus. These carcinogens also decrease herpes and vaccinia virus yields in liquid medium, without affecting Sindbis virus yields. Four structurally related, but noncarcinogenic polycyclic hydrocarbons, namely benzo[e]pyrene, pyrene, benz[a]anthracene and anthracene, have no inhibitory effect on DNA virus replication. Taken together with the known inhibition of interferon production, these effects on virus growth resemble the action of actinomycin D and hence provide evidence for a selective interaction of these carcinogens with DNA.