Pol of gag-pol fusion protein required for encapsidation of viral RNA of yeast L-A virus.
Double-stranded RNA viruses have an RNA-dependent RNA polymerase activity associated with the viral particles which is indispensable for their replication cycle. Using the yeast L-A double-stranded RNA virus we have investigated the mechanism by which the virus encapsidates its genomic RNA and RNA polymerase. The L-A gag gene encodes the principal viral coat protein and the overlapping pol gene is expressed as a gag-pol fusion protein which is formed by a -1 ribosomal frameshift. Here we show that Gag alone is sufficient for virus particle formation, but that it fails to package the viral single-stranded RNA genome. Encapsidation of the viral RNA requires only a part of the Pol region (the N-terminal quarter), which is presumably distinct from the RNA polymerase domain. Given that the Pol region has single-stranded RNA-binding activity, these results are consistent with our L-A virus encapsidation model: the Pol region of the fusion protein binds specifically to the viral genome (+) strand, and the N-terminal gag-encoded region primes polymerization of Gag to form the capsid, thus ensuring the packaging of both the viral genome and the RNA polymerase.
Fujimura
T
T
Departamento de Microbiología y Genética, CSIC/Universidad de Salamanca, Spain.
Ribas
J C
JC
Makhov
A M
AM
Wickner
R B
RB
D000595:Amino Acid Sequence; D001483:Base Sequence; D002213:Capsid / Q000378:metabolism*; D004252:DNA Mutational Analysis; D015683:Gene Products, gag / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D012328:RNA Viruses / Q000235:genetics*; D012330:RNA, Double-Stranded / Q000235:genetics*; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D013329:Structure-Activity Relationship; D014760:Viral Fusion Proteins / Q000378:metabolism*; D014779:Virus Replication
D015683:Gene Products, gag; D009838:Oligodeoxyribonucleotides; D012330:RNA, Double-Stranded; D014760:Viral Fusion Proteins; D012324:RNA-Dependent RNA Polymerase