PROTEIN UBIQUITINATION IN THE POSTERIOR SILK GLANDS OF BOMBYX-MORI

Ubiquitin gene expression and the ubiquitination of proteins in the po sterior silk glands (PSG) of B. mori were analyzed developmentally wit h respect to fibroin synthesis and degeneration. Two ubiquitin transcr ipts are expressed throughout larval stages, and the level of each tra nscript is regulated differently. The larger transcript, a polyubiquit in mRNA, was abundant during the molt stage, while levels of the small er ubiquitin transcript increased immediately after molting. Only a si ngle 65 kDa ubiquitinated protein was detected late in the 5th instar, and the amount increased up to spinning stage. This ubiquitinated pro tein may participate in the PSG degeneration.