Escape from R-peptide deletion in a γ-retrovirus

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• The R peptide in the cytoplasmic tail (C-tail) of gamma-retroviral envelope proteins (Env) is known to inhibit membrane fusion prior to viral budding.
• Understanding the precise role of the R peptide in the formation of infectious viral particles is crucial for retroviral research.

Purpose of the Study:

• To investigate the function of the R peptide in the cytoplasmic tail of gibbon ape leukaemia virus (GaLV) Env proteins during the assembly of replication-competent murine leukaemia viruses (MLVs).
• To analyze the impact of R peptide deletion on viral particle formation, infectivity, and spreading.

Main Methods:

• Construction of chimeric MLVs using GaLV Env proteins, with either intact or R-peptide deleted C-tails.
• Analysis of viral titers, spreading efficiency, and characterization of escape mutants.
• Assessment of Env protein expression, particle incorporation, and intracellular co-localization with Gag proteins.

Main Results:

• Deletion of the R peptide did not affect viral titers but significantly impaired viral spreading.
• An escape mutant with a restored open reading frame for a C-terminal extension of the C-tail was identified, which restored viral replication.
• The escape Env protein exhibited enhanced expression and restored intracellular co-localization with Gag proteins, leading to effective particle incorporation.

Conclusions:

• The R peptide plays a dual role in gamma-retrovirus replication, regulating both membrane fusion and efficient Env protein incorporation into viral particles.
• C-terminal modifications or extensions of the Env C-tail can compensate for the loss of the R peptide, restoring viral infectivity and spreading.