Immunoelectron microscopy of aldehyde-fixed yeast cells.

Immunolocalization of antigens in cells requires simultaneous preservation of structure and antigenicity. The difficulties of immunolocalization methods are centered around the methods used to preserve structure, which as a rule tend to degrade the ability of antigens (usually proteins) to be recognized by their cognate antibodies. The value of immunolocalization for cell biology was early recognized in the case of yeast at the level of the light microscope: immunolocalizations and, even more important, colocalizations using reagents labeled differentially with different fluorophores were developed and came into general use in the early 1980sJ -4 However, application of immunolocalization in electron microscopy of yeast lagged behind, largely because of the difficulty of adequately preserving both structure and antigenicity with the sample preparation methods then in general use. The advent of useful immunoelectron microscopy (immuno-EM) for yeast was the realization by van Tuinen and Riezman 5 that sodium metaperiodate (NalO4) can be used to facilitate the infiltration of resin into intact yeast cells (i.e., cells with their cell walls in place). Robin Wright (working in Jasper Rine's laboratory) used this method with a variety of new acrylic resins just coming into use and found that one of them, L.R. White, gives particularly good results with metaperiodate-treated yeast cells. 6 We adopted Wright's technique and, over the last decade, have optimized and extended it so that we can now routinely preserve structures and still see most antigens, with a frequency of successful localization comparable to that reported for other cell types, including mammalian cells. 7-11 The critical element