RESUMO
In the family Bromoviridae, a mixture of the three genomic RNAs of bromo-, cucumo-, and oleaviruses is infectious as such, whereas the RNAs of alfamo- and ilarviruses require binding of a few molecules of coat protein (CP) to the 3' end to initiate infection. Most studies on the early function of CP have been done on the alfamovirus Alfalfa mosaic virus (AMV). The 3' 112 nucleotides of AMV RNAs can adopt two different conformations. One conformer consists of a tRNA-like structure that, together with an upstream hairpin, is required for minus-strand promoter activity. The other conformer consists of four hairpins interspersed by AUGC-sequences and represents a strong binding site for CP. Binding of CP to this conformer enhances the translational efficiency of viral RNAs in vivo 40-fold and blocks viral minus-strand RNA synthesis in vitro. AMV CP is proposed to initiate infection by mimicking the function of the poly(A)-binding protein.
Assuntos
Alfamovirus/fisiologia , Proteínas do Capsídeo/metabolismo , Ilarvirus/fisiologia , Replicação Viral , Alfamovirus/genética , Proteínas do Capsídeo/genética , Regulação Viral da Expressão Gênica , Genoma Viral , Ilarvirus/genética , Doenças das Plantas/virologiaRESUMO
Alfamo- and ilarviruses are characterized by the deficiency of their genomes (three messenger-sense RNAs) to start an infection cycle. The RNAs are in capsids built from a single species of protein of about 24 kD. A few dimers of this coat protein per RNA molecule are sufficient to activate the genome. Since the first description of genome activation [Bol JF, van Vloten-Doting L, Jaspars EMJ (1971) Virology 46: 73-85] three models have been proposed concerning its mechanism: the protection, the replicase and the messenger release hypotheses. The first two models make use of the fact that in these genera of RNA viruses the 3' termini of the RNAs bind the coat protein very strongly. The resulting structure would provide protection against 3'- to 5' exoribonucleases, or would permit correct initiation of minus-strand synthesis, respectively. However, naked inoculated RNAs of alfalfa mosaic virus appear to be quite stable in the cell, and in vitro the coat protein is inhibiting rather than stimulating initiation of minus-strand synthesis. The messenger release hypothesis states that the coat protein is needed for the release of viral messenger RNAs from membranous replication complexes throughout the whole viral replication cycle. This is supported by in vivo and in vitro observations, but as yet a detailed molecular mechanism is difficult to give.
Assuntos
Alfamovirus/genética , Regulação Viral da Expressão Gênica , Genoma Viral , Ilarvirus/genética , Alfamovirus/fisiologia , Capsídeo/metabolismo , Ilarvirus/fisiologia , RNA Mensageiro/genética , RNA Viral/genética , RNA Viral/metabolismo , Replicação ViralRESUMO
The coat protein (CP) of alfalfa mosaic virus was used as a carrier molecule to express antigenic peptides from rabies virus and HIV. The antigens were separately cloned into the reading frame of alfalfa mosaic virus CP and placed under the control of the subgenomic promoter of tobacco mosaic virus CP in the 30BRz vector. The in vitro transcripts of recombinant virus with sequences encoding the antigenic peptides were synthesized from DNA constructs and used to inoculate tobacco plants. The plant-produced protein (virus particles) was purified and used for immunization of mice. Both antigens elicited specific virus-neutralizing antibodies in immunized mice.