Signal peptides and signal peptidase in Drosophila melanogaster.

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Abstract
Translation of poly(A)-containing RNA from the female fat body of D. melanogaster in a rabbit reticulocyte cell-free system results in the synthesis of previtellogenin polypeptides (pV) having higher apparent MW (46,000 and 45,000) than the forms seen after an in vivo pulse labeling. When this RNA is translated in the presence of EDTA-stripped microsomal membranes from the dog pancreas, vitellogenin precursors are produced that upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, comigrate with the in vivo forms (apparent MW 45,000 and 44,000). These processed forms are sequestered within the microsomal lumen, as evidenced by their insensitivity to trypsin digestion. Neither processing nor sequestration occur posttranslationally. A microsomal membrane fraction derived from Drosophila embryos cotranslationally processes the PVs and a murine pre-light chain IgG. These observations support a signal-mediated mode of secretion in Drosophila. Signal sequence recognition and signal peptidase activities may be conserved even between mammalian and insect systems.