A Sec62p-related component of the secretory protein translocon from Drosophila displays developmentally complex behavior.

The isolation and characterization of a Drosophila melanogaster gene (Dtrp1) that encodes a protein displaying the properties of both a structural and functional homolog of the yeast endoplasmic reticulum membrane-bound translocation protein Sec62p is reported. We show that Dtrp1 can not only rescue the lethality associated with a SEC62 gene knockout in yeast, but also complement the sec62-associated defective transport of a precursor polypeptide from the cytoplasm into the lumen of the endoplasmic reticulum. Expression of the Dtrp1 gene throughout Drosophila development is characterized by peaks in mid-embryo-genesis and mid-pupation, followed by a sustained period of mRNA accumulation in adults. The examination of male reproductive tissues showed a very high level of preferential expression of a 1.6 kb message, while a 2.2 kb message was confined almost exclusively to the non-reproductive tissues. Within the reproductive tract itself the 1.6 kb message was expressed in testes, ejaculatory duct and particularly strongly in the paragonial glands. Since these latter organs are specialized secretory tissues we suggest that the 1.6 kb message may encode a protein isoform that performs a unique, tissue-specific role in the protein translocation pathway. Such observations may indicate a hitherto unexpected diversity in components of the protein translocation pathway in respect to stage, tissue and, potentially, substrate specificity.