Investigating the mechanisms used by the Adenovirus E4-34kDa protein to promote viral late gene expression
Abstract (Summary)Adenovirus (Ad) early region 4 (E4) is important for normal viral DNA accumulation, late mRNA stability, late protein synthesis and virus particle assembly. The 34kDa protein encoded by E4 open reading frame 6 (E4-34kDa) and the 11kDa protein encoded by E4 open reading frame 3 (E4-11kDa) have redundant functions and each is sufficient to replace E4 functions during Ad infection. The E4-34kDa protein forms a complex with the 55kDa protein from early region 1b (E1b-55kDa). This complex promotes the post-transcriptional accumulation of viral late mRNA in the cytoplasm while subsequently inhibiting cellular mRNA nuclear export. E4-34kDa and E1b-55kDa have leucine-rich nuclear export signals and shuttle between the nucleus and the cytoplasm as a complex. E1b-55kDa binds RNA nonspecifically and together these observations suggested a direct role for E4-34kDa and E1b-55kDa in viral mRNA export. The importance of E4-34kDa nuclear localization signals for promoting viral late gene expression of a defective E4 mutant virus was determined. An E4-34kDa NES mutant promoted viral late gene expression as well as the wild type E4-34kDa protein. Further genetic analysis of the E4-34kDa protein revealed that central regions of the protein important for binding the E1b-55kDa protein as well as forming a complex with a cellular E3 ubiquitin ligase were critical for E4-34kDa to promote Ad late gene expression. This E4-34kDa/E1b-55kDa/E3 ubiquitin ligase complex ubiquitinates the tumor suppressor p53, and targets it for proteasome-mediated degradation during Ad infection. The ability of E4-34kDa to target proteins for proteasome-mediated degradation was required for promoting viral late gene expression, even in the absence of p53, suggesting that p53 was not the critical degradation target for expression of late genes. Viruses which expressed the E4-11kDa protein were able to express viral late proteins in the presence of proteasome inhibitors, whereas proteasome inhibitors dramatically affected the ability of an E4-11kDa virus mutant to express its late genes. Therefore, in the absence of the redundant functions of the E4-11kDa protein, E4-34kDa/E1b-55kDa promotion of viral late gene expression requires active proteasomes.
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2003