The Golgi matrix is a collection of proteins involved in the structure and function of the Golgi apparatus. The matrix was first isolated in 1994 as an amorphous collection of 12 proteins that remained associated together in the presence of detergent (which removed Golgi membranes) and 150 mM NaCl (which removed weakly associated proteins). Treatment with a protease enzyme removed the matrix, which confirmed the importance of proteins for the matrix structure. Modern freeze etch electron microscopy (EM) clearly shows a mesh connecting Golgi cisternae and associated vesicles. Further support for the existence of a matrix comes from EM images showing that ribosomes are excluded from regions between and near Golgi cisternae.