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J Cell Sci. 1994 Apr;107 ( Pt 4):923-32.

A chimera of the cytoplasmic tail of the mannose 6-phosphate/IGF-II receptor and lysozyme localizes to the TGN rather than prelysosomes where the bulk of the endogenous receptor is found.

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Medical Research Council, Laboratory of Molecular Biology, Cambridge, UK.


We fused the cytoplasmic and transmembrane domains of the bovine mannose 6-phosphate/IGF-II receptor (MPR) to lysozyme, a monomeric secretory protein thought to be devoid of sorting information. When the resulting chimera (lys/MPR) was transiently expressed in COS cells or stably expressed in CV1 cells, it had a predominantly intracellular distribution in the trans-Golgi region, with less than 10% present on the surface. In contrast, a similar chimera containing the transmembrane and cytoplasmic domains of the low density lipoprotein receptor (lys/LDLR) was localized to the plasma membrane, even though it endocytoses efficiently. Exchanging domains between the lys/MPR and lys/LDLR chimeras indicated that the MPR cytoplasmic domain contains the information necessary to specify the intracellular localization of the chimeric molecule. This signal must be located in the membrane-proximal third of the tail, as deletion of the last 120 residues of the 163 residue tail has no obvious effect on the distribution of lys/MPR. However, the recycling of the lys/MPR does not completely mimic that of the intact endogenous MPR, as immunofluorescence labelling shows that they are predominantly in different locations, indicating a role for the lumenal domain of the MPR in determining the steady-state distribution of the MPR itself.

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