Fig. 1. Confocal fluorescence microscopy of HEK293T cells transfected with expression constructs. Scale bars, 20 µm. A. Transfection with plasmid encoding fluorescent protein AvicFP-ER localized to ER (green channel). B. Cotransfection with plasmids encoding AvicFP-ER (green channel) and M-protein. C. Cotransfection with plasmids encoding AvicFP-ER (green channel) and M-protein with subsequent immunostaining for M-protein (red channel; a merged channel image is shown on the right). The images are collages of four (A), four (B) and two (C) fields of view, showing representative results of each experiment.

Fig. 2. A scheme of SARS-CoV-2 М-protein intermembrane oligomerization. A. Stacking of ER membranes into OSER structure through interactions of М-protein dimers in adjacent membranes. B. Hypothetical participation of the М-protein intermembrane oligomers in the neck formation during budding (М-protein molecules at other locations are omitted for clearance).