Gamma Interferon-Treated Mouse L929 Cells

a site of macromolecular synthesis with the established IFN.y-induced inhibition of rickettsial growth. A method was developed to measure the syntheses of DNA, rRNA, and protein by R. prowazekii during a 2-h pulse-labeling period while the rickettsiae were growing within cultured host cells that had intact macromolecular synthesis. This method involved incubation of the rickettsia-infected cells with a radioactive precursor (H332Po4 or Tran3MS-label), purification of the rickettsiae, purification of rickettsial nucleic acids, and analysis of rickettsial nucleic acids and proteins by electrophoresis and autoradiography. A key feature of the method involved the use of calculated specific activities from a densitometric analysis of gels and autoradiograms, a procedure that made the data independent of rickettsial recovery. Rickettsial DNA and rRNA syntheses were both inhibited 12 h after the addition of IFN-y to infected cultures, whereas the synthesis of rickettsial proteins was not inhibited at this time. In contrast, at 20 h after the addition of IFN-y, rickettsial DNA, rRNA, and protein syntheses were all inhibited.