Enhanced iron uptake of Saccharomyces cerevisiae by heterologous expression of a tadpole ferritin gene

We genetically engineered Saccharomyces cerevisiae to express ferritin, a u biquitous iron storage protein, with the major heavy-chain subunit of tadpo le ferritin. A 450-kDa ferritin complex tan store up to 4,500 iron atoms in its central cavity. We cloned the tadpole ferritin heavy-chain gene (TFH) into the yeast shuttle vector YEp352 under the control of a hybrid alcohol dehydrogenase II and glyceraldehyde-3-phosphate dehydrogenase promoter. We confirmed transformation and expression by Northern blot analysis of the re combinant yeast, by Western blot analysis using an antibody against Escheri chia coli-expressed TFH, and with Prussian blue staining that indicated tha t the yeast-expressed tadpole ferritin was assembled into a complex that co uld bind iron. The recombinant yeast was more iron tolerant in that 95% of transformed cells, but none of the recipient strain cells, could form colon ies on plates containing 30 mM ferric citrate. The cell-associated concentr ation of iron was 500 mug per gram (dry cell weight) of the recombinant yea st but was 210 mug per gram (dry cell (weight) in the wild type. These find ings indicate that the iron-carrying capacity of yeast is improved by heter ologous expression of tadpole ferritin and suggests that this approach may help relieve dietary iron deficiencies in domesticated animals by the use o f the engineered yeast as a feed and food supplement.