Abstract
The developmental profiles of ultraspiracle protein (USP) in the tissues of Drosophila melanogaster were investigated using a USP specific monoclonal antibody (mAb) as a probe. Western blot analysis revealed four USP mAb reactive bands (p46, p48, p54 and p56), each with tissue- and stage-specific expression patterns. The p54 and p56 were expressed in nearly all larval and prepupal tissues tested with fluctuations in abundance. However, the p46 and p48 were detected exclusively in the midgut of prepupae and shown to be the proteolytic products of p54 and p56. A lambda protein phosphatase assay demonstrated that the p56 is the phosphorylated form of p54. The expression and phosphorylation of the p54 USP is regulated by 20E. Protein kinase consensus recognition sequence analysis revealed 10 putative phosphorylation sites in Drosophila USP, with seven sites for protein kinase C (PKC) and three sites for casein kinase II (CKII). The fact that seven out of 10 putative phosphorylation sites reside in the ligand- and DNA-binding domains suggests that phosphorylation may play important role in regulating USP function. Identification of the in vivo USP phosphorylation sites and signal transduction pathways that regulate the specific USP phosphorylation is currently underway.
