Inhibition of HeLa cell protein synthesis during adenovirus infection: Restriction of cellular messenger RNA sequences to the nucleus

The mechanism by which adenovirus type 2 inhibits HeLa cell protein synthesis has been investigated by a quantitative analysis of the synthesis and metabolism of cellular and viral hnRNA † † Abbreviations used: hnRNA, heterogeneous nuclear RNA; cDNA, complementary DNA. sequences. By the time labeling of cellular proteins is maximally inhibited, 16 hours following adenovirus infection under the conditions we have used, all of the newly made messenger RNA sequences reaching the cytoplasm are viral-specific. Thus, the gradual shift from translation of cellular to translation of viral mRNA species that begins following entry of adenovirus-infected cells into the late phase of the productive cycle, can probably be explained simply by competition between the two types of mRNA for available ribosomes. In order to investigate the mechanism(s) by which adenovirus infection exerts this dramatic change in the biogenesis of HeLa cellular mRNA sequences, the hnRNA fraction has been isolated quantitatively from infected cells after pulselabeling or a pulse-chase. Cellular and viral transcripts were then distinguished by hybridization to viral DNA. The results of these experiments reveal that the rate of synthesis of cellular hnRNA sequences remains constant throughout the course of adenovirus type 2 infection. Moreover, poly(A) is apparently added normally to cellular hnRNA sequences synthesized during the late phase of productive adenovirus infection. This newly synthesized, poly(A)-containing hnRNA cannot be distinguished from the corresponding fraction isolated from mockinfected cells by hybridization to cDNA prepared using uninfected HeLa cell, cytoplasmic, poly(A)-containing RNA as template: it also appears to be metabolized with kinetics similar to those observed in uninfected cells.