Immunoelectron microscopic exploration of the Golgi complex.

Using immunogold labeling of ultrathin cryosections, we have studied the localization of secretory, lysosomal, and membrane proteins in the Golgi complexes of several cell types. All proteins were present in the stacks of Golgi cisternae, illustrating that the cisternae comprise a ubiquitous way station for proteins with multiple destinations. The labeling patterns support the concept that peripheral Golgi vesicles represent the main site of secretory protein concentration. Of the membrane proteins studied, the Golgi enzyme galactosyltransferase was confined to the trans-most few cisternae, whereas the receptors for asialoglycoproteins and for polymeric immunoglobulin A occurred in most cisternae, with increasing concentration approaching the trans side. The findings are discussed in relation to a cisternal cis to trans progression of Golgi cisternae and membrane specificity.