I don't know anything about yeast, but a number of filamentous fungi have modified to overexpress proteins of various sorts, including for human food. Some of this is reviewed in Trinci, A.P.J. 1995. Pure and Applied Mycology. Canadian J. Bot. 73 (Supplement 1): S1-S14. Good Luck! todell at u.washington.edu Mycology is better than Urology!