A gene regulating the time dependence of alpha-L-fucosidase concentration is closely linked with the structural gene in man.

The dependence of the specific activities of human alpha-L-fucosidase and four other lysosomal glycosidases on cell growth was determined in long-term lymphoid cell lines in which the polymorphic forms of alpha-L-fucosidase were identified by isoelectric focusing. In cultured lymphoblasts of Fu-1 phenotype the alpha-L-fucosidase synthesis during cell growth was found to be proportional to the general amount of protein. However, in cells derived from individuals possessing at least one FUCA*2 allele, the amount of enzyme increased progressively during the log-phase of growth, reaching a maximum at the transition to the stationary phase. The maximum increase of enzyme concentration was observed in the mid-log phase of exponential growth. The results may be explained by the existence of a regulatory locus FUCT which maps in close proximity to the structural gene. The FUCT locus which controls the amount of enzyme in the cell appears to be specific for alpha-L-fucosidase.