The small envelope protein E is not essential for murine coronavirus replication.

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• The small envelope (E) protein is recognized as important for coronavirus assembly and virion morphogenesis.
• Previous studies demonstrated defects in viral growth and aberrant virion assembly in mouse hepatitis virus (MHV) with E gene mutations.

Purpose of the Study:

• To investigate the essentiality of the E protein in MHV replication by generating a viable mutant lacking the E gene.
• To characterize the properties of a MHV mutant with a deleted E gene.

Main Methods:

• Targeted RNA recombination was employed to generate a MHV mutant (Delta E) with the entire E gene deleted.
• A host range-based selection system was utilized for mutant generation.
• Phenotypic characterization included plaque morphology, growth rate, infectious titer, and genetic stability assessments.

Main Results:

• A viable MHV mutant (Delta E) lacking the E gene, along with nonessential upstream genes 4 and 5a, was successfully generated.
• The Delta E mutant exhibited significantly reduced growth rate, low infectious titer, and produced tiny plaques with unusual morphology.
• Despite phenotypic alterations, the Delta E mutant demonstrated genetic stability over multiple passages.

Conclusions:

• The E protein plays a significant role in MHV replication and virion assembly, as evidenced by the Delta E mutant's properties.
• Surprisingly, the E protein is not essential for MHV viability, as a viable mutant lacking the E gene could be generated and maintained.