MICROSOMAL ALDEHYDE DEHYDROGENASE IS LOCALIZED TO THE ENDOPLASMIC-RETICULUM VIA ITS CARBOXYL-TERMINAL-35 AMINO-ACIDS

Rat microsomal aldehyde dehydrogenase (msALDH) has no amino-terminal s ignal sequence, but instead it has a characteristic hydrophobic domain at the carboxyl terminus (Miyauchi, K., R. Masaki, S. Taketani, A. Ya mamoto, A. Akayama, and Y. Tashiro. 1991. J. Biol. Chem. 266:19536-195 42), This membrane-bound enzyme is a useful model protein for studying posttranslational localization to its final destination. When express ed from cDNA in COS-1 cells, wild-type msALDH is localized exclusively in the well-developed ER. The removal of the hydrophobic domain resul ts in the cytosolic localization of truncated proteins, thus suggestin g that the portion is responsible for membrane anchoring. The last 35 amino acids of msALDH, including the hydrophobic domain, are sufficien t for targeting of E. coli beta-galactosidase to the ER membrane. Furt her studies using chloramphenicol acetyltransferase fusion proteins su ggest that two hydrophilic sequences on either side of the hydrophobic domain play an important role in ER targeting.