THE REGULATORY CHARACTERISTICS OF YEAST FRUCTOSE-1,6-BISPHOSPHATASE CONFER ONLY A SMALL SELECTIVE ADVANTAGE

The question of how the loss of regulatory mechanisms for a metabolic enzyme would affect the fitness of the corresponding organism has been addressed. For this, the fructose-1,6-bisphosphatase (FbPase) from Sa ccharomyces cerevisiae has been taken as a model. Yeast strains in whi ch different controls on FbPase (catabolite repression and inactivatio n; inhibition by fructose-2,6-bisphosphate and AMP) have been removed have been constructed. These strains express during growth on glucose either the native yeast FbPase, the Escherichia coli FbPase which is i nsensitive to inhibition by fructose-2,6-bisphosphate, or a mutated E. coil FbPase with low sensitivity to AMP. Expression of the heterologo us FbPases increases the fermentation rate of the yeast and its genera tion time, while it decreases its growth yield. In the strain containi ng high levels of an unregulated bacterial FbPase, cycling between fru ctose-6-phosphate and fructose-1,6-bisphosphate reaches 14%. It is sho wn that the regulatory mechanisms of FbPase provide a slight but defin ite competitive advantage during growth in mixed cultures.