title: Segregation of mutant ovalbumins and ovalbumin-globin fusion proteins in Xenopus oocytes. Identification of an ovalbumin signal sequence.
abstract: The intramolecular signals for chicken ovalbumin secretion were examined by producing mutant proteins in Xenopus oocytes. An ovalbumin complementary DNA clone was manipulated in vitro, and constructs containing altered protein-coding sequences and either the simian virus 40 (SV40) early promoter or Herpes simplex thymidine kinase promoter, were microinjected into Xenopus laevis oocytes. The removal of the eight extreme N-terminal amino acids of ovalbumin had no effect on the segregation of ovalbumin with oocyte membranes nor on its secretion. A protein lacking amino acids 2 to 21 was sequestered in the endoplasmic reticulum but remained strongly associated with the oocyte membranes rather than being secreted. Removal of amino acids 231 to 279, a region previously reported to have membrane-insertion function, resulted in a protein that also entered the endoplasmic reticulum but was not secreted. Hybrid proteins containing at their N terminus amino acids 9 to 41 or 22 to 41 of ovalbumin fused to the complete chimpanzee alpha-globin polypeptide were also sequestered by oocyte membranes. We conclude that the ovalbumin "signal" sequence is internally located within amino acids 22 to 41, and we speculate that amino acids 9 to 21 could be important for the completion of ovalbumin translocation through membranes.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002499:Centrifugation, Density Gradient; D002872:Chromosome Deletion; D005260:Female; D005914:Globins / Q000235:genetics*; D008566:Membranes / Q000032:analysis; D009154:Mutation; D009865:Oocytes; D010047:Ovalbumin / Q000235:genetics* / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D014982:Xenopus laevis / Q000235:genetics
chemical_list: D014415:Tunicamycin; D005914:Globins; D010047:Ovalbumin