Visualization of the lymphocytic choriomeningitis mammarenavirus (LCMV) genome reveals the early endosome as a possible site for genome replication and viral particle pre-assembly.

We report a fluorescence hybridization (FISH) assay that allows the visualization of lymphocytic choriomeningitis mammarenavirus (LCMV) genomic RNAs in individual cells. We show that viral S segment genomic and antigenomic RNA, along with viral nucleoprotein, colocalize in subcellular structures we presume to be viral replication factories. These viral RNA structures are highly dynamic during acute infection, with the many small foci seen early coalescing into larger perinuclear foci later in infection.