Regulation of the expression of cathepsin B in Sarcophaga peregrina (flesh fly) at the translational level during metamorphosis.

Previously, we reported that cathepsin B of pupal hemocytes participates in dissociation of the fat body of Sarcophaga larvae at metamorphosis. In this study, we demonstrated that the amount of cathepsin B in hemocytes was controlled at the translational level, i.e. larval hemocytes stored a significant amount of untranslated cathepsin B mRNA. When the larvae pupated, translation of the mRNA commenced, resulting in accumulation of cathepsin B. Our results indicate that the 3'-untranslated region (3'-UTR) of this mRNA is necessary for the repression of its translation in a rabbit reticulocyte lysate. We detected the 3'-UTR binding protein in the lysate of larval hemocytes, but not in the pupal hemocytes. The role of this protein in the translation of cathepsin B mRNA is discussed.