Disease relevance of ORF1b

• ORF1b is probably expressed via a +1 ribosomal frameshift mechanism, most similar to that of lettuce infectious yellows virus (LIYV) [1].
• This putative protein contains the array of methyltransferase, RNA helicase, and RNA-dependent RNA polymerase domains that is conserved in the Sindbis-like supergroup of positive-strand RNA viruses [2].
• Phylogenetic analysis of the three replication-associated domains, MT, HEL, and RdRp, indicates that CTV and BYV form a separate closterovirus lineage within the alpha-like supergroup of positive-strand RNA viruses [3].
• Amino acid sequences of the MTR, HEL, and RdRp show highly significant similarity to the homologous sequences from other closteroviruses and lower similarity to the respective proteins of tobamoviruses, tobraviruses, hordeiviruses, bromoviruses, and furoviruses [4].

High impact information on ORF1b

• This genome organization is typical of the monopartite closteroviruses, including the putative +1 ribosomal frameshift allowing expression of ORF1b [5].
• In the positive-stranded RNA genome of beet yellows closterovirus (BYV), the 5'-terminal ORF 1a encodes a 295 kDa polyprotein with the domains of papain-like cysteine proteinase, methyltransferase (MT) and helicase (HEL), whereas ORF 1b encodes an RNA-dependent RNA polymerase [6].
• Computer-assisted analysis of LIYV RNA 1 ORFs identified domains for a papain-like protease, methyltransferase (MTR), RNA helicase (HEL), and RNA-dependent RNA polymerase (RdRp) [4].
• An incomplete ORF, ORF1, encoded the C-terminal part of a putative RNA-dependent RNA polymerase, most closely related to polymerases of tricornaviruses; the putative product of ORF3, 65K, was found to be a homologue of the hsp70 family of cell heat-shock proteins [7].

Biological context of ORF1b

• The expression of ORF1b may be via a +1 ribosomal frameshift mechanism, similar to other closteroviruses [8].

References