Figure 10. Identification of possible double-helical stems corresponding to those seen in the crystal structure.

There are 30 stems in the crystal structure, each containing nine base pairs with an additional base stacked at each 3′ end, i.e., 20 nucleotides (Figure 1). A model that connects successive stems would require something on the order of 5–10 nucleotides per connection. This figure shows how our secondary structure model might be organized to fit into the STMV capsid, with a sufficient number of stems to cover the 30 edges of the icosahedral frame, as required by Figure 1.