Discrimination between Functional and Non-functional Cellular Gag Complexes involved in HIV-1 Assembly

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Human immunodeficiency virus type 1 (HIV-1) Gag and Gag-Pol proteins are essential for viral assembly and maturation.
• Intracellular Gag-containing complexes (GCCs) are found in Gag-expressing cells, but their function in HIV assembly remains unclear.

Purpose of the Study:

• To investigate the composition and role of GCCs in HIV-1 assembly.
• To differentiate between on-pathway and off-pathway Gag-containing complexes.

Main Methods:

• Sucrose gradient ultracentrifugation of cellular lysates from Gag-expressing cells.
• Analysis of GCC composition, focusing on Gag oligomerization state and association with cellular machinery like ribosomes.

Main Results:

• The majority of identified GCCs consist of monomeric or dimeric Gag bound to ribosomal complexes, indicating they are not direct precursors for virion assembly.
• A subset of large GCCs (over 20 Gag molecules) may represent genuine on-pathway intermediates, potentially equivalent to previously identified membrane-associated puncta.

Conclusions:

• Most GCCs are not on-pathway intermediates but rather a reservoir of Gag proteins that can be recruited for assembly.
• This study provides a framework for understanding the heterogeneity of GCCs and identifying early on-pathway intermediates in HIV-1 assembly.