Functional Characterization of Kaposi's Sarcoma-Associated Herpesvirus ORF45 byBacterial Artificial Chromosome-Based Mutagenesis

• Published in: Journal of virology 2006-12, Vol.80 (24), p.12187-12196
• Main Authors: Zhu, Fan Xiu, Li, Xiaojuan, Zhou, Fuchun, Gao, Shou-Jiang, Yuan, Yan
• Format: Article
• Language: English
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.01275-06

Open reading frame 45 (ORF45) of Kaposi's sarcoma-associated herpesvirus (KSHV) encodes an immediate-early protein. This protein is also present in virions as a tegument protein. ORF45 protein interacts with interferon regulatory factor 7 (IRF-7) and inhibits virus-induced type I interferon production by blocking activation of IRF-7. To define further the function of ORF45 and the mechanism underlying its action, we constructed an ORF45-null recombinant virus genome (BAC-stop45) by using a bacterial artificial chromosome (BAC) system. Stable 293T cells carrying the BAC36 (wild type) and BAC-stop45 genomes were generated. When monolayers of 293T BAC36 and 293T BAC-stop45 cells were induced with 12- O -tetradecanoylphorbol-13-acetate and sodium butyrate, no significant difference was found between them in overall viral gene expression and lytic DNA replication, but induced 293T BAC-stop45 cells released 10-fold fewer virions to the medium than did 293T BAC36 cells. When ORF45-null virus was used to infect cells, lower infectivity was observed than for wild-type BAC36. These results suggest that KSHV ORF45 plays roles in both early and late stages of viral infection, probably in viral ingress and egress.