prM-E heterodimerization of prM mutants with inserted alanine as a percentage of the binding intensity of wild type prM. Each prM to E ratio was calculated. The wild type prM/E ratio was taken as 100% in evaluating the mutant prM-E binding affinity. Each data represents the average of the experiments for a single prM mutant and the error is standard deviation. The positions of the alanine insertions in the TM region of prM are indicated.