Counteraction by 20-hydroxyecdysone of the effect of juvenile hormone on phosphorylation of ribosomal protein S6.

Phosphorylation of ribosomal protein S6, induced when the fat body of Sarcophaga peregrina (flesh-fly) larvae was incubated in vitro in the presence of 32P, was found to be suppressed by juvenile hormone. This suppressive effect of juvenile hormone was counteracted by a physiological concentration of 20-hydroxyecdysone. Since 20-hydroxyecdysone is known to induce phosphorylation of S6 in vivo, this reaction was suggested to be regulated by the balance of the effects of ecdysone and juvenile hormone.