Replication of Togaviruses and Flaviviruses
المؤلف:
Stefan Riedel, Jeffery A. Hobden, Steve Miller, Stephen A. Morse, Timothy A. Mietzner, Barbara Detrick, Thomas G. Mitchell, Judy A. Sakanari, Peter Hotez, Rojelio Mejia
المصدر:
Jawetz, Melnick, & Adelberg’s Medical Microbiology
الجزء والصفحة:
28e , p560-561
2025-12-13
35
The alphavirus RNA genome is positive sense (Figure 1). Genomic-length and subgenomic (26S) mRNAs are produced during transcription. The genomic-length transcript pro duces a precursor polyprotein encoding the nonstructural proteins (ie, replicase and transcriptase) needed for viral RNA replication. The subgenomic mRNA encodes structural proteins. The proteins are elaborated by posttranslational cleavage. Alphaviruses replicate in the cytoplasm and mature by budding nucleocapsids through the plasma membrane. Sequence data indicate that western equine encephalitis virus is a genetic recombinant of eastern equine encephalitis and Sindbis viruses.
Fig1. Genomic organization of alphaviruses. The nonstructural proteins (nsP) are translated from the genomic RNA as a polyprotein that is processed into four nonstructural proteins by a viral protease present in nsP2. The structural proteins are translated from a subgenomic 26S mRNA as a polyprotein that is processed by a combination of viral and cellular proteases into a capsid protein (C), three envelope glycoproteins (E3, E2, and E1), and a membrane-associated protein named 6K. C, E2, and E1 are major components of virions and are shaded in the figure. (Reproduced with permission from Strauss JH, Strauss EG, Kuhn RJ: Budding of alphaviruses. Trends Microbiol 1995;3:346.)
The flavivirus RNA genome also is positive sense. A large precursor protein is produced from genome-length mRNAs during viral replication; it is cleaved by viral and host proteases to yield all the viral proteins, both structural and nonstructural. Flaviviruses replicate in the cytoplasm, and particle assembly occurs in intracellular vesicles (Figure 2). Proliferation of intracellular membranes is a characteristic of flavivirus-infected cells.
Fig2. The flavivirus life cycle. (Courtesy of CM Rice.)
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