Toxoplasma gondii: Growth in the absence of host cell protein synthesis |
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Authors: | ER Pfefferkorn Lorraine C Pfefferkorn |
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Institution: | Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755, U.S.A. |
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Abstract: | Host cell protein synthesis continues when cultured cells are infected by Toxoplasma gondii. In order to determine if this host function is necessary for the parasite we used two independent methods that specifically block cellular protein synthesis. In the first, we infected a temperature-sensitive Chinese hamster ovary cell mutant that has a thermolabile leucyl tRNA synthetase. At the restrictive temperature of 40 C, the mutant cells showed only negligible protein synthesis that was probably mitochondrial. At this temperature, the growth and nucleic acid synthesis of T. gondii proceeded normally and 3H]leucine was specifically incorporated into the parasite as demonstrated by autoradiography. A secpnd method for blocking protein synthesis by the host cell employed treatment of uninfected human fibroblast cells with muconomycin A, an inhibitor of initiation. Repeated washing of monolayer cultures reduced the free muconomycin A to an insignificant level while the cells remained incapable of protein synthesis. T. gondii infected and grew normally in the inhibited cells. Autoradiographic localization of the incorporation of 3H]leucine showed that it was almost exclusively in the intracellular parasites in the cells pretreated with muconomycin A. In the untreated control most of the 3H]leucine was incorporated by the host cell rather than the parasite. We conclude that de novo protein synthesis by the host cell is not required to support the growth of intracellular T. gondii. |
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Keywords: | Protozoa parasitic Cell culture Fibroblast human Chinese hamster ovary cell wild type Chinese hamster ovary cell temperaturesensitive mutant in protein synthesis Muconomycin A Protein synthesis |
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