title: The open reading frame 5A of foxtail mosaic virus is expressed in vivo and is dispensable for systemic infection.
abstract: Infectious transcripts were successfully derived from full-length cDNA clones of foxtail mosaic potexvirus (FoMV). Full-length clones were constructed by RT-PCR whereby 5' and 3' genomic segments of 2.7 and 3.4 kb, respectively, were ligated into Bluescript II KS. The in vitro RNA transcripts were infectious to moncotyledonous (barley) and dicotyledonous (Chenopodium amaranticolor) plant species. Individual mutation studies on clones of each of the five major ORFs confirmed predicted gene function for the polymerase, TGB (triple gene block), and coat protein (CP) genes. Protoplast studies on expression of a unique open reading frame, ORF 5A, which initiates 143 nts upstream of the CP before it "reads through" the CP, revealed that the 5A protein was produced in vivo. Mutation analysis of the 5A ORF indicated, however, that it was not required for either replication or for productive infection of plants. However, the nucleic acid sequences encoding the extended CP segment were shown to be important for CP expression. Additional mutations in 5A had no effect on FoMV replication in protoplasts but rendered the virus noninfectious to plants. A correlation with diminished CP production from both mutant clones implies that synthesis of subgenomic CP mRNA was compromised, and this limited systemic infection.
authors.affiliation: United States Department of Agriculture-Agricultural Research Service, Palmer, Alaska, USA.
authors.forename: N L
authors.initials: NL
authors.lastname: Robertson
authors.forename: R
authors.initials: R
authors.lastname: French
authors.forename: T J
authors.initials: TJ
authors.lastname: Morris
mesh_terms: D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D015153:Blotting, Western; D002213:Capsid / Q000032:analysis / Q000235:genetics; D003001:Cloning, Molecular; D017931:DNA Primers; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D018274:Electroporation; D005814:Genes, Viral; D009154:Mutation; D016366:Open Reading Frames; D010944:Plants / Q000821:virology*; D017863:Potexvirus / Q000235:genetics* / Q000378:metabolism; D011523:Protoplasts / Q000821:virology; D012333:RNA, Messenger / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D017931:DNA Primers; D012333:RNA, Messenger; D012367:RNA, Viral; D012321:DNA-Directed RNA Polymerases