Trimer oligomerization on 125-nt ssDNA. Silver stained polyacrylamide gel of half of the indicated reactions electrophoresed under reducing and denaturing conditions. Except for lane 4 and the insert, the indicated amounts of ORF1p trimer were incubated in 15 μl with either 0.125 μM of a single stranded-oligonucleotide (Supplementary Table S1, #1) in 50 mM NaCl or in 0.5 M NaCl for 20 min at room temperature and then cross-linked for 30 min with 1.0 mM of the bifunctional EGS reagent and then processed for electrophoresis as described in the ‘Materials and Methods’ section. The protein in lane 4 and those in the insert, at 0.189 μM, were incubated with 0.015 mM EGS, which partially cross-links the trimer or polymers thereof giving a ladder of products on denaturing gels equivalent in size to monomern—indicated by the numbers to the left of lane 4 and the insert. Each lane of the insert contains the entire sample. The gels were imaged as described in Ref. 35 and the scans are shown in Supplementary Figure S2.