Related Experiment Videos
The double-stranded RNA genome of yeast virus L-A encodes its own putative RNA polymerase by fusing two open reading
1Section on Genetics of Simple Eukaryotes, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Abstract:
The L-A double-stranded RNA virus of Saccharomyces cerevisiae encodes its major coat protein (80 kDa) and a minor single-stranded RNA binding protein (180 kDa) that has immunological cross-reactivity with the major coat protein. The sequence of L-A cDNA clones revealed two open reading frames (ORF), ORF1 and ORF2. These two reading frames overlap by 130 base pairs and ORF2 is in the -1 reading frame with respect to ORF1. Although the major coat protein of the viral particles is encoded by ORF1, the 180-kDa protein is derived from the entire double-stranded RNA genome by fusing ORF1 and ORF2, probably by a -1 translational frameshift. Within the overlapping region is a sequence similar to that producing a -1 frameshift by "simultaneous slippage" in retroviruses. The coding sequence of ORF2 shows a pattern characteristic of viral RNA-dependent RNA polymerases of icosahedral (+)-strand RNA viruses. Thus, the 180-kDa protein is analogous to gag-pol fusion proteins.
Insights
The Saccharomyces cerevisiae L-A virus generates a minor 180-kDa protein via a -1 translational frameshift, fusing two open reading frames (ORF1 and ORF2). This protein shares immunological properties with the major coat protein.
Area of Science:
- Virology
- Molecular Biology
- Yeast Genetics
Background:
- The L-A virus in Saccharomyces cerevisiae is a double-stranded RNA virus.
- It encodes an 80-kDa major coat protein and a 180-kDa minor single-stranded RNA binding protein.
- The minor protein shows immunological cross-reactivity with the major coat protein.
Purpose of the Study:
- To elucidate the genetic basis for the production of the 180-kDa protein from the L-A virus.
- To understand the relationship between the two open reading frames (ORFs) and their encoded proteins.
- To investigate the mechanism of protein synthesis and its implications for viral structure and function.
Main Methods:
- Sequencing of L-A cDNA clones to identify open reading frames (ORFs).
- Analysis of the overlapping region between ORF1 and ORF2.
- Comparison of ORF2 coding sequence with known viral RNA-dependent RNA polymerases.
Main Results:
- Two overlapping ORFs (ORF1 and ORF2) were identified in the L-A virus genome.
- ORF1 encodes the major 80-kDa coat protein.
- The 180-kDa protein is produced by a -1 translational frameshift, fusing ORF1 and ORF2, a mechanism similar to retroviral frameshifting.
- ORF2's sequence resembles RNA-dependent RNA polymerases of icosahedral (+)-strand RNA viruses.
Conclusions:
- The 180-kDa protein is a gag-pol fusion protein analog, arising from a programmed -1 frameshift during translation.
- This frameshifting mechanism is crucial for generating the diverse protein components of the L-A virus.
- The findings provide insights into viral gene expression strategies and protein evolution in RNA viruses.