Figure 1.

(A) Schematic representation of PS1. The critical aspartates in TM 6 and 7 as well as the endoproteolytic cleavage site(s) (arrow) and the mutations introduced at codon 286 are indicated. (B) Expression and endoproteolytic processing of the mutant PS1 derivatives (CT, untransfected control expressing endogenous PS). Cell lysates were immunoprecipitated with antibody 3027, and precipitated PS1 derivatives (CTFs and holoprotein) were visualized by immunoblotting using antibody BI.3D7. *, Phosphorylated PS1 CTF (13, 36). Note that endoproteolysis of PS1 occurs in all cell lines investigated. (C) Overexpressed mutant PS1 derivatives displace endogenous PS2 CTFs. Cell lysates were immunoblotted with the monoclonal antibody BI.HF5c.