GENES AND CIS-ACTING SEQUENCES INVOLVED IN REPLICATION OF BARLEY YELLOW DWARF VIRUS-PAV RNA

Deletion and point mutation analyses were employed to determine gene p roducts and cia-acting signals involved in translation, replication, a nd encapsidation of barley yellow dwarf virus (PAV serotype) RNA in oa t protoplasts. Of the six open reading frames (ORFs), only ORFs 1 and 2, which include the putative RNA-dependent RNA polymerase gene, were required for replication. In vitro translation of these mutants reveal ed that sequence upstream of the shifty heptanucleotide was required f or ribosomal frameshifting, and that a 3'-translational enhancer stimu lated translation more efficiently when located in closer proximity to the translated ORFs. Deletion of the coat protein gene reduced the ac cumulation of genomic but not subgenomic RNA. The carboxy-terminally e xtended form of the coat protein, produced by readthrough of its stop codon, was not required for encapsidation. Although the ORF6 product w as not necessary, cis-acting RNA signals in and around ORF6 were requi red for RNA replication. Defective RNAs harboring various deletions we re not replicated in trans by the co-inoculated wild-type helper genom e, suggesting that replication of PAV RNA may be coupled to translatio n. (C) 1995 Academic Press, Inc.