The Golgi enzyme UDP-GlcNAc-lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-1-phosphotransferase), an alpha2beta2gamma2 hexamer, mediates the initial step in the addition of the mannose 6-phosphate targeting signal on newly synthesized lysosomal enzymes []. GNPTAB encodes the alpha and beta subunits of GlcNAc-1-phosphotransferase, and mutations in this gene cause the lysosomal storage disorders mucolipidosis II and III alpha-beta. The alpha-beta subunits contain three identifiable domains separated by so-called spacer regions. This domain is part of the first spacer region, Spacer-1 []. Studies indicate that GlcNAc-1 lacking spacer-1 exhibits enhanced phosphorylation of several non-lysosomal glycoproteins, while the phosphorylation of lysosomal acid hydrolases is not altered. In view of these effects on the maturation and function of GlcNAc-1, it is suggested to rename 'spacer-1' the 'regulatory-1' domain [].
