I. The Moroccan Jewish population has an elevated incidence of Tay-Sachs disease. We have examined 6 unrelated Moroccan carriers of the disease and have identified three HEXA gene mutations: (1) a Leu(181)->Stop mutation in one carrier, (2) an Arg(170)->Glu change in two of the carriers and (3) an in-frame deletion of a phenylalanine codon at position 304 (delta-F) in three of the carriers. II. The complete organization of the murine HEXB gene and the majority of the HEXA gene has been established. This has allowed the construction of gene targeting vectors for the purpose of "knocking out" the HEX genes in mouse embryonic stem cells and for ultimately producing mouse models of the G(M2) gangliosidoses. III. Mechanisms by which normal and abnormal proteins are retained in the endoplasmic reticulum (ER) have been determined. The protein signals that specify whether members of a family of carboxylesterases are secreted or retained in the ER have been identified. These retention signals are variants of the yeast signal (HDEL) previously thought not to function in mammalian cells. We have also found that the unglycosylated alpha-subunit of beta- hexosaminidase undergoes an altered folding pathway resulting in the formation of an insoluble, inappropriately disulfide-bonded aggregate that is retained in the ER. The inappropriately folded protein is bound to BiP/GRP 70 which acts as a molecular scaffold in ER.