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Protein and RNA synthesis by isolated Rickettsia prowazekii

Purified host-cell-free Rickettsia prowazekii synthesized protein from leucine, lysine, or proline as radioactive precursor. Most, if not all, of the rickettsial proteins were synthesized. The specific activities of the newly synthesized proteins in the cytoplasmic fraction and in the envelope fraction were not significantly different, indicating that both soluble and envelope proteins were synthesized and the latter were inserted into the envelope. The synthesis of protein was sensitive to chloramphenicol but insensitive to the eucaryotic inhibitors cycloheximide and atractyloside. When added before the initiation of synthetic activity, rifampin, a transcriptional inhibitor, inhibited protein synthesis as quickly and extensively as did chloramphenicol, a translational inhibitor. However, when added during synthetic activity, rifampin, unlike chloramphenicol, allowed protein synthesis to continue for several minutes. These results indicate that de novo transcription is necessary for de novo translation and that no stable mRNA pool exists in these rickettsiae. UMP was incorporated into both rRNA and mRNA. The minimal conditions necessary for RNA synthesis contrasted with the complex medium required for protein synthesis. The half-life of the labeled RNA synthesized in these rickettsiae was approximately 16 min. It was concluded that all the rickettsial mRNA that had existed in the growing intracellular rickettsiae was degraded during their lengthy purification.