Role of the nucleocapsid region in HIV-1 Gag assembly as investigated by quantitative fluorescence-based microscopy

•Quantitative fluorescence microscopy techniques are highly useful to evidence the role of NC during Gag assembly.•These techniques allow directly visualizing and evidencing Gag-Gag interactions in a cellular context.•Combination of FRET with fluorescence lifetime imaging is especially powerful for monitoring Gag assembly in live cells.•The NC domain of Gag is an important determinant for HIV-1 and RSV viral assembly.

The Gag precursor of HIV-1, formed of the four proteic regions matrix (MA), capsid (CA), nucleocapsid (NC) and p6, orchestrates virus morphogenesis. This complex process relies on three major interactions, NC-RNA acting as a scaffold, CA-CA and MA-membrane that targets assembly to the plasma membrane (PM). The characterization of the molecular mechanism of retroviral assembly has extensively benefited from biochemical studies and more recently an important step forward was achieved with the use of fluorescence-based techniques and fluorescently labeled viral proteins. In this review, we summarize the findings obtained with such techniques, notably quantitative-based approaches, which highlight the role of the NC region in Gag assembly.