Abstract:
This study aimed to identify whether the signature of phosphorylation or dephoshorylation of the proteins involved in glucose sensing, signal transduction and glucose repression pathways can be observed at the transcription of the genes encoding those proteins. S. cerevisiae BY4743 strains (ho /ho , hap4 /hap4 , rip1 /rip1 and RIP1/rip1 ) were cultivated under nitrogen limited condition in order to identify the variations in the expression levels of genes involved in glucose sensing, signal transduction and glucose repression pathways as a response to system level perturbations. Metabolite profiles for glucose, ethanol, ammonia and glycerol were obtained as well as the growth curves. Expression profiles of CYC8, GRR1, MTH1, RGT1, RGT2, SKP1, SNF3, STD1,TUP1, YCK1, YCK2, ELM1, GLC7,HXK2, MIG1, PAK1, REG1, SNF1, SNF4, TOS3, HAP4, MBA1 genes were determined. The cell densities of the ho /ho , rip1 /rip1 and RIP1/rip1 mutants decreased whereas growth of hap4 /hap4 mutant increased in response to nitrogen pulse. Highest cell density was obtained in ho /ho and hap4 /hap4 strains at the second steady state. The ethanol production was higher in respiratory deficient hap4 /hap4 and rip1 /rip1 mutants. Glycerol production was significantly lower in RIP1 mutations in comparison to the other studied strains. The expression level of MIG1, MBA1, GRR1 and REG1 increased in response to nitrogen pulse in all studied mutants. RIP1 deletion resulted in the repression of HAP4, MTH1, SKP1 RGT1, MBA1 and YCK1 genes. Respiratory deficiency seems to affect the expression of RGT1, MBA1 and may be the reason for the dissimilarity observed between the expression profiles of MIG1-HXK2, GRR1-SKP1 and MIG1-CYC8-TUP1. The deletion of HAP4 does not seem to affect significantly the expression patterns of REG1, GLC7, MIG1, SNF1 and SNF4. HAP4 seems to plays an important role in nitrogen catabolite repression in yeast. Deletion of RIP1 seems to affect the transcriptional response of HAP4 in nitrogen catabolite repression in yeast.
