Host-genotype and agent effects in scrapie incubation: Change in allelic interaction with different strains of agent

Summary Incubation period in mice of ME7 scrapie agent is known to be controlled by the gene sinc. Evidence is presented that the same gene probably also determines incubation period for the 22A scrapie agent which has very different biological properties. Not only is there a reversal of the direction of gene effect when these agents are compared in mice homozygous for two different alleles of sinc, but there is also a different type of allelic interaction—absence of dominance with ME7 and overdominance with 22A. Other agents are mentioned which extend this range of allelic interaction even further. It is suggested that replication of scrapie agent depends on a multimeric host site and that the two alleles of sinc contribute different types of subunits to these sites.