DNA Degradation by Adenovirus in Permissive and Non-Permissive Infections

Abstract

<p>The adenovirus type 2 (Ad2) lp mutants: lp3, lp5, and the Ad2 deletion mutant, dl250, all have altered early region ElB sequences which affect the encoded 19K product. Alkaline sucrose gradient analysis shows that DNA degradation occurs in permissive human (KB) cells infected by Ip3 at high temperatures (39ºC), but not at lower temperatures. This indicates a thermolabile 19K product which is altered in its ability to prevent DNA degradation. The Ip5 virus did not induce DNA degradation in KB cells at all temperatures tested, in contrast to the results from the 19K negative mutant dl250, in which extensive DNA degradation ocurred. Results showed that the Ad2 lp3 or dl250 viral yields were not drastically reduced despite the DNA degradation phenotypes. Thus the 19K product is not essential for viral production although it does inhibit intracellular DNA degradation.</p> <p>The DNA degradation phenotype was also observed in wildtype Ad12 infections of the non-permissive monkey cell line, CV1. Analysis of viral specific protein and RNA expression in the Ad12 infected CV1 cells suggest that the level of EIB expression was reduced in these non-permissive cells when compared to expression in permissive (KB) cells. Expression of the other early regions was slightly reduced in the CV1 cells compared to that in Ad12 infected KB cells. Despite expression of most early regions and normal DNA replication, adenoviral late gene expression was very much reduced in CV1 cells. This may be a result of reduced amounts of E1B 55K and/or E4 products which are required for efficient: transport and translation of late viral messages.</p> <p>DNA degradation was also assayed in CV1 cells infected by one of two recombinant viruses: T1227 or T2743. These viruses had Ad12 E1A, or Ad12 F1A and E1B sequences, respectively, replacing the equivalent sequences in an Ad5 virus background. The latter virus codes for a complete Ad12 19K product, the former an Ad5 19K. Degradation induced by both viruses suggests that the Ad12 E1A has a nuclease effector function which is not completely inhibited by the Ad5 19K in CV1 cells.</p>