A -1 ribosomal frameshift in a double-stranded RNA virus of yeast forms a gag-pol fusion protein.
The L-A double-stranded RNA (dsRNA) virus of Saccharomyces cerevisiae has two open reading frames (ORFs). ORF1 encodes the 80-kDa major coat protein (gag). ORF2, which is expressed only as a 180-kDa fusion protein with ORF1, encodes a single-stranded RNA-binding domain and has the consensus sequence for RNA-dependent RNA polymerases of (+)-strand and double-stranded RNA viruses (pol). We show that the 180-kDa protein is formed by -1 ribosomal frame-shifting by a mechanism indistinguishable from that of retro-viruses. Analysis of the "slippery site" suggests that a low probability of unpairing of the aminoacyl-tRNA from the 0-frame codon at the ribosomal A site reduces the efficiency of frameshifting more than the reluctance of a given tRNA to have its wobble base mispaired. Frameshifting of L-A requires a pseudoknot structure just downstream of the shift site. The efficiency of the L-A frameshift site is 1.8%, similar to the observed molar ratio in viral particles of the 180-kDa fusion protein to the major coat protein.
Dinman
J D
JD
Section on the Genetics of Simple Eukaryotes, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Icho
T
T
Wickner
R B
RB
D000595:Amino Acid Sequence; D001483:Base Sequence; D016368:Frameshift Mutation; D015685:Fusion Proteins, gag-pol / Q000235:genetics*; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015345:Oligonucleotide Probes; D016366:Open Reading Frames; D010957:Plasmids; D014176:Protein Biosynthesis; D012328:RNA Viruses / Q000235:genetics*; D012330:RNA, Double-Stranded / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014158:Transcription, Genetic
D015685:Fusion Proteins, gag-pol; D015345:Oligonucleotide Probes; D012330:RNA, Double-Stranded