SARS-CoV-2 nsp3 and nsp4 are minimal constituents of a pore spanning replication organelle

Coronavirus replication is associated with the remodeling of cellular membranes, resulting in the formation of double-membrane vesicles (DMVs). A DMV-spanning pore was identified as a putative portal for viral RNA. However, the exact components and the structure of the SARS-CoV-2 DMV pore remain to be determined. Here, we investigate the structure of the DMV pore by in situ cryo-electron tomography combined with subtomogram averaging. We identify non-structural protein (nsp) 3 and 4 as minimal components required for the formation of a DMV-spanning pore, which is dependent on nsp3-4 proteolytic cleavage. In addition, we show that Mac2-Mac3-DPUP-Ubl2 domains are critical for nsp3 oligomerization and crown integrity which influences membrane curvature required for biogenesis of DMVs. Altogether, SARS-CoV-2 nsp3-4 have a dual role by driving the biogenesis of replication organelles and assembly of DMV-spanning pores which we propose here to term replicopores. Coronavirus RNA replication is governed by membrane vesicles containing pores. The authors used in situ cryo-electron tomography to reveal the minimal constituents of a SARS-CoV-2 “replicopore” and its role in the formation of replication vesicles.