Deoxycytidine is salvaged not only into DNA but also into phospholipid precursors. II. Ara-C does not inhibit the later process in lymphoid cells.

dCTP formed from exogenous deoxycytidine via the salvage pathways was previously shown to serve deoxyliponucleotide synthesis in lymphocytes (Spasokukotskaja et al, Biochem. Biophys. Res.

Cellular regulation of ADP-ribosylation of proteins. III. Selective augmentation of in vitro ADP-ribosylation of histone H3 in murine thymic cells after in vivo emetine treatment.

Thymic cells were isolated at intervals of between 0 and 144 h from mice that received one intraperitoneal injection of emetine (33 mg/kg), and thymus weight, incorporation of [14C]leucine into proteins and [3H]thymidine into DNA in intact thymic cells, as well as initial rates of protein ADP-ribosylation in permeabilized cells [A. Sóoki-Tóth, F. Asghari, E.

Cellular regulation of poly ADP-ribosylation of proteins. II. Augmentation of poly(ADP-ribose) polymerase in SV40 3T3 cells following methotrexate-induced G1/S inhibition of cell cycle progression.

SV40-3T3 cells were exposed in monolayer cultures to 5 X 10(-7) M methotrexate (MTX), that inhibited thymidylate synthetase, arrested cell growth without cell killing in 24 h and did not induce single- (ss) or double-strand (ds) breaks in DNA. Following 24, up to 72 h, the poly(ADP-ribose) polymerase content of attached cells was induced by 5 X 10(-7) M MTX and the augmentation of the enzyme increased with the time of exposure to the drug. Inhibition of protein or RNA synthesis abolished augmentation of enzymatic activity; so too did the initiation of maximal cell growth by thymidine + hypoxanthine, by-passing the inhibitory site of MTX.

The immunosuppressive effect of acute doses of emetine on murine thymic cells.

Emetine--a general inhibitor of protein synthesis--was investigated for its ability to depress specific immune response in animal models. A single dose (33 mg/kg) of emetine administered subcutaneously to mice markedly decreased thymus weight and thymic cell numbers. DNA, RNA and protein synthesis of thymic cells were reduced by 90, 50 and 65%, respectively.

Poly(ADP-ribose) and replicative DNA synthesis studied in permeable mouse thymocytes.

Poly(ADP-ribose) and DNA synthesis were followed in a random population of freshly isolated and permeabilized mouse thymocytes. Different conditions were found to be optimal for the synthesis of poly(ADP-ribose) and DNA, respectively. The suspension of one of the processes did not influence significantly the synthesis of the other macromolecule.