The LEA-like protein HSP 12 in Saccharomyces cerevisiae has a plasma membrane location and protects membranes against desiccation and ethanol-inducedstress

The LEA-like protein HSP 12 was identified as having a plasma membrane loca tion in yeast. Gold particles, indicative of the presence of HSP 12, were o bserved on the external side of the plasma membrane when yeast grown to sta tionary phase were subjected to immunocytochemical analysis, Growth of yeas t in the osmolyte mannitol resulted in an increased number of gold particle s that were now observed to be present on both sides of the plasma membrane . No gold particles were observed using a mutant strain of the same yeast t hat did not express HSP 12. A model liposome system encapsulating the fluor escent dye calcein was used to investigate the protection by HSP 12 of memb ranes during desiccation, HSP 12 was found to act in an analogous manner to trehalose and protect liposomal membrane integrity against desiccation. Th e interaction between HSP 12 and the liposomal membrane was judged to be el ectrostatic as membrane protection was only observed with positively charge d liposomes and not with either neutral or negatively charged liposomes. Th e ability of the wild-type and mutant yeast to grow in media containing eth anol was compared. It was found that yeast not expressing the HSP 12 protei n were less able to grow in media containing ethanol. HSP 12 was shown to c onfer increased integrity on the liposomal membrane in the presence of etha nol. Ethanol, like mannitol, was found to induce HSP 12 protein synthesis. However, yeast grown in both ethanol and mannitol showed a decreased HSP 12 response compared with yeast grown in the presence of either osmolyte alon e. (C) 2000 Elsevier Science B.V. All rights reserved.