An icosahedral shell with 60 each of three nonidentical polypeptide chains must contain at least four intersubunit bonds. A set of four connections defines a minimal bonding network. A classification scheme has been devised to count all of the minimal bonding networks; it has been found that there are 240 distinct possible four-bonded nets. The data of the previous paper by Scraba and co-workers (Hordern, Leonard, and Scraba, 1979, Virology97, 131-140) suggest that such an approach to the description of the picornavirus capsid might have validity. In turn, the minimal bonding net theory can be applied to the data obtained for the Mengo virion. The results of such an analysis suggest that, of the 240 possible minimal nets, there are two minimal nets that are completely consistent with the data obtained. Because the analysis is general and complete, there are no other possibilities. Deciding between the two remaining possible minimal nets will require further experiments. © 1979.
