Watching one's P's and Q's: promiscuity, plasticity, and quasiequivalence in a T = 1 virus.

Although quasiequivalence is not needed to explain the assembly of the T = 1 canine parvovirus capsid, the interactions of the 60-fold symmetrical capsid protein with less symmetrical viral components illustrate the elements of plasticity and promiscuity of interactions that are embodied in quasiequivalence. The current analysis is based on interactions of fivefold related proteins with a single peptide running along the fivefold axis, and on interactions of the capsid protein with various fragments of the genomic DNA, each having a different sequence and exposing the protein to interactions with different types of nucleotide base.