Global gene expression in recombinant and non-recombinant yeast Saccharomyces cerevisiae in three different metabolic states

Global gene expression of two strains of Saccharomyces cerevisiae. one recombinant (P+). accumulating large amounts of an intracellular protein Superoxide Dismutase (SOD) and one non-recombinant (P)which does not contain the recombinant plasmid, were compared In batch Culture during drauxic growth when cells were growing exponentially on glucose, when they were growing exponentially on ethanol, and ill the early stationary phase when glycerol was being utilized When comparing the gene expression for P- (and P+) during growth oil ethanol to that on glucose (Eth/Gluc), overexpression is related to an increase in consumption of glycerol, activation of the TCA cycle, degradation of glycogen and metabolism of ethanol Furthermore, 97 6% of genes (80 genes) involved in the central metabolic pathway are overexpressed This is similar to that observed by DeRisi et al. [DeRisi, J L, Iyer, V.R & Brown, P.O. 1997. Exploring the metabolic and genetic control of gene expression oil a genomic scale Science 278 680-686] but very different from was observed for Metabolic Flux Analysis (MFA), where the specific growth rate is lowered to ca. 40%, the fluxes in the TCA cycle are reduced to ca 40% (to 30% in P+), glycolysis is reduced to Virtually 0 and protein synthesis to ca 50% (to 40%. in P+) Clearly it Is not possible to correlate in a simple or direct way, quantitative mRNA expression levels with cell function which is shown by the Metabolic Flux Analysis (MFA). When comparing the two strains in the 3 growth stages. 4 genes were found to be Under or overexpressed in all cases The products of all of these genes are expressed at the plasma membrane or cell wall of the yeast. While comparing the strains (P+/P-) when growing oil glucose, ethanol and in the early stationary phase. many of the genes of the central metabolic pathways are underexpressed in P+, which is similar to the behaviour of the metabolic fluxes of both strains (MFA). Comparing the gene expression for P- (and to sonic extent P+) during the early stationary phase to growth oil ethanol (Stat/Eth). underexpression is generalized. This shows that the switch in metabolism between ethanol and early stationary phases has ail almost instantaneous effect on gene expression but a much more retarded effect oil metabolic fluxes and that the early stationary phase represents a late ethanol phase from the metabolic analysis point of view since ethanol is still present and being consumed although at a much Slower late (C) 2009 Elsevier Inc. All rights rescived.