MONOCLONAL-ANTIBODY HFD9 IDENTIFIES A NOVEL 28 KDA INTEGRAL MEMBRANE-PROTEIN ON THE CIS-GOLGI

We have raised a monoclonal antibody (mAb) (HFD9) that detects a 28 kD a protein (p28) enriched in the Golgi membrane. p28 was localized to t he perinuclear Golgi region in all cell lines thus far examined. Its G olgi localization was confirmed by its colocalization with Golgi marke rs using indirect immunofluorescence microscopy. Immunogold labelling demonstrates that the majority of p28 was localized on the cis-Golgi a nd its associated structures. Two independent experiments demonstrate that the p28 epitope recognized by mAb HFD9 is exposed to the cytosol. Extraction of Golgi membranes with a variety of reagents revealed tha t p28 behaves like an integral membrane protein. mAb HFD9 thus defines a novel 28 kDa integral membrane protein on the cis-Golgi. To our kno wledge, p28 represents the first integral membrane protein of the Golg i system identified via the antibody approach whose epitope is cytopla smically-oriented and highly-conserved. Monoclonal antibody HFD9 will thus provide a useful tool for further studies on the cis side of the Golgi, which is not well characterised due to the lack of good markers .