Illustration of revolution versus rotation motion. Spooling of the genome inside the procapsid supports the revolution mechanism. A. Rotation resembles the Earth’s motion about its axis once every 24 hours, while revolution resembles the Earth ‘circling’ around the Sun once every 365 days (see animations: http://nanobio.uky.edu/movie.html). B. (a) Cyro-EM images of phi29 particles in a cut-away surface showing the formation of a empty DNA toroidal ring. Due to the persistence length of dsDNA, which is around 150 bp, it is impossible for dsDNA to form a ring with a radius of only 0.9-2.9 nanometers without wrapping around protein. Since Cryo-EM picture is the average of many images, the toroid formation could be resulted from a collective image of many dsDNA revolving steps. (b) Cyro-EM images showing the spooling motion of phi29 genome during packaging as a result of the revolution motion. (Figure 1A: Adapted from  with permission of BioMed Central; Figure 1B: a. Adapted from  with permission of BioMed Central and from  with permission of Elsevier; b. Adapted from  with permission of Elsevier).