Mapping the rubella virus subgenomic promoter

Area of Science:

• Virology
• Molecular Biology
• RNA Virus Replication

Background:

• Rubella virus (RUB), a Togaviridae family member, synthesizes subgenomic (SG) RNA for virion protein production.
• SG RNA synthesis is directed by the SG promoter (SGP) located on a negative-strand template.

Purpose of the Study:

• To precisely map the Rubella virus SG promoter (SGP) and identify its essential elements for SG RNA synthesis and virus viability.

Main Methods:

• Utilized infectious cDNA vectors (dsRobo402/GFP) with duplicated SGP regions for initial mapping.
• Employed replicon vectors (RUBrep/GFP, RUBrep/CAT) and a wild-type infectious clone (Robo402) for refined SGP analysis.
• Performed 5' deletions and internal deletions within the putative SGP region to assess functional impact on RNA synthesis and virus replication.

Main Results:

• The minimal RUB SGP was mapped from nucleotide -26 to +6 relative to the SG start site.
• Deletions upstream of -26 in replicon vectors abolished SG RNA synthesis.
• Deletions upstream of -28 in the infectious clone impaired virus viability, highlighting the importance of this region.
• A repeated UCA triplet at the 5' end of SG RNA was found to be essential.

Conclusions:

• The RUB SGP is located immediately adjacent to the SG start site, similar to alphaviruses, but lacks sequence homology.
• The minimal functional SGP spans nucleotides -26 to +6, with a broader region necessary for efficient virus replication.
• Understanding the SGP is crucial for elucidating Rubella virus replication mechanisms.