Alteration with age of symbiosis of gene expression in aphid endosymbionts.

Aphid endosymbionts in vivo in young hosts synthesized almost exclusively only one protein, symbionin. The synthesis of symbionin declined with age of the host and instead the endosymbiont began to express some of its own genes which were expressed in vitro but were repressed in vivo in young host. A prolonged treatment of young host with cycloheximide brought about a physiological state similar to that in old insect. Though in the very old insect symbionin was no longer produced by its endosymbiont, the host seemed to depend almost entirely upon the gene products of the endosymbiont.