Sterols have been found to occur in almost all eucaryotic as well as a few procaryotic organisms. With the exception of the hormonal rolesl, few studies have addressed the non- structural roles for sterols in the cells. Working with a specially constructed yeast sterol auxotroph, least four functions for sterols in that organism have now been defined. It has become obvious that there is an intimate relationship between regulation of sterol synthesis and heme competency. This relationship will be explored further in this study. Using immunocytochemical and radio-labeling techniques, the cellular location of ergosterol will be determined. This will be related to sterol functions and the yeast cell cycle. The function of the sterol C5=6 unsaturation will be probed. Finally, an interesting mutation allowing an apparent decrease in structural specificity for sterol functions will be studied. The proposed research is a part of an overall objective of understanding the role of sterols in the general economy of the cell. Yeast is ideally suited for the research because of its ease of culture, the well-defined genetic and molecular biological procedures, and the wealth of biochemical data that is available on this organism.***
