Turnip yellow mosaic virus: transfer RNA mimicry, chloroplasts and a C‐rich genome

Abstract

SUMMARY Taxonomy: Turnip yellow mosaic virus (TYMV) is the type species of the genus Tymovirus, family Tymoviridae. TYMV is a positive strand RNA virus of the alphavirus‐like supergroup. Physical properties: Virions are non‐enveloped 28‐nm T = 3 icosahedrons composed of a single 20‐kDa coat protein that is clustered in 20 hexameric and 12 pentameric subunits. Infectious particles and empty capsids coexist in infected tissue. The genomic RNA is 6.3 kb long, with a 5′m7GpppG cap and a 3′ untranslated region ending in a tRNA‐like structure to which valine can be covalently added. The genome has a distinctive skewed C‐rich, G‐poor composition (39% C, 17% G). Viral proteins: Two proteins, whose open reading frames extensively overlap, are translated from the genomic RNA. p206, which contains sequences indicative of RNA capping, NTPase/helicase and polymerase activities, is the only viral protein that is necessary for genome replication in single cells. It is produced as a polyprotein and self‐cleaved to yield 141‐ and 66‐kDa proteins. p69 is required for virus movement within the plant and is also a suppressor of gene silencing. The coat protein is expressed from the single subgenomic RNA. Hosts and symptoms: TYMV has a narrow host range almost completely restricted to the Cruciferae. Experimental host species are Brassica pekinensis (Chinese cabbage) or B. rapa (turnip), in which diffuse chlorotic local lesions and systemic yellow mosaic symptoms appear. Arabidopsis thaliana can also be used. Clumping of chloroplasts and the accumulation of vesicular invaginations of the chloroplast outer membranes are distinctive cytopathological symptoms. High yields of virus are produced in all leaf tissues, and the virus is readily transmissible by mechanical inoculation. Localized transmission by flea beetles may occur in the field.

Characterization of a Replication Element in the Coat Protein ORF of Turnip Yellow Mosaic Virus

“…TYMV is a non-enveloped icosahedral virus that contains a monopartite 6.3 kb genomic RNA (gRNA) that encodes p206 (replicase), p69 (movement protein), and coat protein (1). The coat protein is expressed from a subgenomic RNA (sgRNA) that is produced during replication of TYMV.…”

Phosphorylation of Viral RNA-dependent RNA Polymerase and Its Role in Replication of a Plus-strand RNA Virus

“…These peptides were further analyzed by PSD in MALDI-TOF MS (15). 9 , which encompasses the N-terminal His tag, was observed as both mono-and bisphosphorylated.…”

“…The genomic RNA of TYMV, a plant-infecting member of the alphavirus-like superfamily of plus-strand RNA viruses (9), encodes two nonstructural proteins of 69 and 206 kDa (206K), the coat protein (CP) being expressed from a subgenomic RNA. 206K, the only viral protein required for TYMV RNA replication, shares considerable sequence similarity with replication proteins of other plus-strand RNA viruses and contains domains indicative of methyltransferase, proteinase, NTPase/helicase, and RdRp activities.…”

Replication and encapsidation of recombinant Turnip yellow mosaic virus RNA

“…The virion has pentameric and hexameric protein aggregates that protrude from the surface and form deep valleys at the quasi three-fold axes (3). TYMV has a single 6.3 kb genomic RNA (gRNA) with an m7 GpppG cap at the 5' end and a tRNA-like structure (TLS) at the 3' end (4). Two proteins, p206 and p69, are translated from the gRNA.…”