SYNTHESIS OF DNA, RIBOSOMAL-RNA, AND PROTEIN BY RICKETTSIA-PROWAZEKIIGROWING IN UNTREATED OR GAMMA INTERFERON-TREATED MOUSE L929-CELLS

The syntheses of DNA, rRNA, and protein by Rickettsia prowazekii growi ng in mouse fibroblastic L929 cells were measured at various times aft er the addition of gamma interferon (IFN-gamma) to correlate the inhib ition of a site of macromolecular synthesis with the established IFN-g amma-induced inhibition of rickettsial growth. A method was developed to measure the syntheses of DNA, rRNA, and protein by R. prowazekii du ring a 2-h pulse-labeling period while the rickettsiae were growing wi thin cultured host cells that had intact macromolecular synthesis. Thi s method involved incubation of the rickettsia-infected cells with a r adioactive precursor ((H3PO4)-P-35, or TranS-35-label), purification o f the rickettsiae, purification of rickettsial nucleic acids, and anal ysis of rickettsial nucleic acids and proteins by electrophoresis and autoradiography. A key feature of the method involved the use of calcu lated specific activities from a densitometric analysis of gels and au toradiograms, a procedure that made the data independent of rickettsia l recovery. Rickettsial DNA and rRNA syntheses were both inhibited 12 h after the addition of IFN-gamma to infected cultures, whereas the sy nthesis of rickettsial proteins was not inhibited at this time. In con trast, at 20 h after the addition of IFN-gamma, rickettsial DNA, rRNA, and protein syntheses were all inhibited.