Posttranscriptional block to synthesis of a human adenovirus capsid protein in abortively infected monkey cells.

Abstract

The synthesis of fiber protein in CV1 (monkey) cells abortively infected with human adenovirus serotype 2 (Ad2) is at least 100-fold less than the synthesis of fiber protein in CV1 cells productively infected with a host range mutant of Ad2 (Ad2hr400) or coinfected with Ad2 plus simian virus 40. However, the amount of fiber mRNA present in the cytoplasm of abortively infected CV1 cells is only 5- to 10-fold less than that in productively infected CV1 cells. Whereas fiber mRNA in abortively infected CV1 cells is utilized poorly as a template for synthesis of fiber protein in vivo, fiber mRNA from abortively infected CV1 cells serves just as efficiently as a template for fiber synthesis in vitro as fiber mRNA from productively infected cells. This was observed both in a nuclease-treated rabbit reticulocyte lysate to which purified fiber mRNA or cytoplasmic ribonucleoprotein complex was added as exogenous template for fiber synthesis, and in S10 extracts of infected CV1 cells utilizing endogenous message as a template. Since translation initiation inhibitors did not diminish synthesis of fiber in S10 extracts of abortively infected CV1 cells, fiber mRNA probably is associated with ribosomes in abortively infected CV1 cells. This conclusion was supported by Northern blot analysis, which showed that in both abortively and productively infected CV1 cells, the same proportion of cytoplasmic fiber mRNA cosedimented with polyribosomes. Although the possibility of extremely rapid fiber turnover in abortively infected monkey cells cannot be rigorously excluded, preliminary data suggest that this is not the case. Thus, these results may imply that translation of the fiber message in abortively infected monkey cells is blocked after formation of the mRNA-ribosome complex.