CHARACTERIZATION OF A CIS-GOLGI MATRIX PROTEIN, GM130

Antisera raised to a detergent- and salt-resistant matrix fraction fro m rat liver Golgi stacks were used to screen an expression library fro m rat liver cDNA. A full-length clone was obtained encoding a protein of 130 kD (termed GM130), the COOH-terminal domain of which was highly homologous to a Golgi human auto-antigen, golgin-95 (Fritzler et al., 1993). Biochemical data showed that GM130 is a peripheral cytoplasmic protein that is tightly bound to Golgi membranes and part of a larger oligomeric complex. Predictions from the protein sequence suggest tha t GM130 is an extended rod-like protein with coiled-coil domains, Immu nofluorescence microscopy showed partial over-lap with medial- and tra ns-Golgi markers but almost complete overlap with the cis-Golgi networ k (CGN) marker, syntaxin5, Immunoelectron microscopy confirmed this lo cation showing that most of the GM130 was located in the CGN and in on e or two cisternae on the cis-side of the Golgi stack. GM130 was not r e-distributed to the ER in the presence of brefeldin A but maintained its overlap with syntaxin5 and a partial overlap with the ER-Golgi int ermediate compartment marker, p53, Together these results suggest that GM130 is part of a cis-Golgi matrix and has a role in maintaining cis -Golgi structure.