title: A conserved, precise RNA encapsidation pattern in Tobamovirus particles.
abstract: The bidirectional RNA encapsidation pathway in nine sequenced Type 1 Tobamovirus genomes will result in RNA-coat protein assembly, up to and including the first transcribed G, adjacent to the 5'-cap structure (m7 Gppp). This precision is highly conserved, despite wide interstrain variations in the absolute position of the phase-determining core of the origin-of-assembly sequence (Gxx)n and in overall genome length (6311-6507 nts). A Type 2 Tobamovirus genome did not comply with this pattern. All genomes had a statistically significant bias for G at every third (or 3n) position, resulting in a preponderance of GNN codons and hence a high Val, Ala, Gly, Asp, Glu content, at least in the large (126/183 kDa) and amino-coterminal replicase protein genes. Contrary to predictions from the X-ray fibre diffraction structure of tobacco mosaic virus (TMV, U1 strain), only one (pepper mild mottle virus) of the nine Type 1 Tobamoviruses positioned the preferred G-repeat in the most favourable (5') position of the trinucleotide binding site on each coat protein (CP) subunit. In all but one of the eight remaining Type 1 Tobamovirus genomes, G would predominate in the CP 3'-site. The significance of these observations for TMV particle assembly, disassembly and host cell interactions are discussed.
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D002213:Capsid / Q000737:chemistry / Q000648:ultrastructure*; D003062:Codon; D005814:Genes, Viral; D008969:Molecular Sequence Data; D009024:Morphogenesis; D012367:RNA, Viral / Q000737:chemistry*; D017898:Tobamovirus / Q000648:ultrastructure*; D015678:Viral Structural Proteins / Q000235:genetics; D014779:Virus Replication
chemical_list: D003062:Codon; D012367:RNA, Viral; D015678:Viral Structural Proteins