Long internal inverted repeat in a yeast viral double-stranded RNA.

Area of Science:

• Virology
• Molecular Biology
• Yeast Genetics

Background:

• Saccharomyces cerevisiae viruses are non-infectious double-stranded (ds) RNA viruses common in laboratory yeast strains.
• Viral particles are primarily composed of a single polypeptide (88 kdaltons) encapsulating dsRNA genomes.

Purpose of the Study:

• To determine the gene location for the capsid polypeptide within the large viral dsRNA (L1) of Saccharomyces cerevisiae.
• To investigate the structure and potential function of an unusual inverted repeat found in L1.

Main Methods:

• Sequencing of cDNA clones homologous to portions of the L1 dsRNA.
• Novel heteroduplex technique for mapping viral RNA sequences.
• Analysis of cDNA sequences for coding regions and structural elements.

Main Results:

• Identified cDNA clones mapping to a region 2.3-2.5 kb from the 5' end of the L1 plus strand, containing stop codons in all reading frames.
• This region is strongly suspected to contain the capsid polypeptide gene.
• Discovered a 170 bp inverted repeat within L1, the longest known non-terminal inverted repeat in viral dsRNA.

Conclusions:

• The capsid polypeptide gene of Saccharomyces cerevisiae viruses is likely located within the 5' 2.3-2.6 kb region of the L1 plus strand.
• The identified inverted repeat may play a role in generating multiple mRNAs from a single viral dsRNA molecule.