Figure 3.

(A) The packaging model. The procapsid shows only binding sites for S at the beginning. After a full size S is packaged, the S sites disappear and M sites appear. After a full size M is packaged, the M sites disappear and L sites appear. After a full size L is packaged, minus-strand synthesis commences. After minus-strand synthesis is completed, plus-strand synthesis commences. (B) If segment S is of the size equal to the sum of both S and M, the S sites will disappear and the L sites will appear and segment L will be packaged without segment M.