Abstract
The influence of adenovirus type 2 infection of HeLa cells upon expression of human histone genes was examined as a function of the period of infection. Histone RNA synthesis was assayed after run-off transcription in nuclei isolated from mock-infected cells and after various periods of adenovirus infection. Histone protein synthesis was measured by [3H]leucine labeling of intact cells and fluorography of electrophoretically fractionated nuclear and cytoplasmic proteins. The cellular representation of RNA species complementary to more than 13 different human histone genes was determined by RNA blot analysis of total cellular, nuclear or cytoplasmic RNA by using a series of 32P-labeled cloned human histone genes as hybridization probes and also by analysis of 3H-labeled histone mRNA species synthesized in intact cells. By 18 h after infection, HeLa cell DNA synthesis and all parameters of histone gene expression, including transcription and the nuclear and cytoplasmic concentrations of core and H1 mRNA species, were reduced to less than 5 to 10% of the control values. By contrast, transcription and processing of other cellular mRNA sequences have been shown to continue throughout this period of infection. The early period of adenovirus infection was marked by an inhibition of transcription of histone genes that accompanied the reduction in rate of HeLa cell DNA synthesis. These results suggest that the adenovirus-induced inhibition of histone gene expression is mediated in part at the transcriptional level. However, the persistence of histone mRNA species at concentrations comparable to those of mock-infected control cells during the early phase of the infection, despite a reduction in histone gene transcription and histone protein synthesis, implies that histone gene expression is also regulated post-transcriptionally in adenovirus-infected cells. These results suggest that the tight coupling between histone mRNA concentrations and the rate of cellular DNA synthesis, observed when DNA replication is inhibited by a variety of drugs, is not maintained after adenovirus infection.