Fig. 1. ACE domain containing 343-655 residues are needed for cleavage secretion of ACE.

A) ACE and its N-terminal deleted mutants were transiently expressed in HeLa cells, labeled with ³⁵S-methionine, and the label was chased for 4 hours, cleavage-secretion was analyzed as described before (27). B) ACE domain containing its 1-655 residues was fused with C-terminal domain of CD4 (312-435 residues), and this chimeric protein was expressed transiently in HeLa cells and its cleavage was tested similarly as in (A). Several other chimeric proteins were generated using ACE residues as shown and were expressed similarly to test their cleavage activity. C) CD4 N-terminal domain (1-352 residues) was fused with C-terminal domain of ACE (343-737) and its cleavage was tested in HeLa cells by similar assay as indicated in (A). Other chimeric proteins were generated by deletion of ACE domain and the CD4 domain as shown and their cleavage was tested in HeLa cells. D) ACE, and ACE/CD4 chimeric proteins (see B and C for residues of ACE and CD4 in the chimera) were transiently expressed in HeLa cells, labeled with ³⁵S-methionine for 30 min and the label was chased for 4 hours. The cell extracts (C) and the culture media (M) were immunoprecipitated with anti-ACE and analyzed by SDS-PAGE and autoradiography.