Differential repression of GAL4 and adjacent transcription activators by operators in the yeast GAL upstream activating sequence

Arabidopsis eIF3e (INT-6) associates with both eIF3c and the COP9 signalosome subunit CSN7

The Arabidopsis COP9 signalosome is a multisubunit repressor of photomorphogenesis that is conserved among eukaryotes. This complex may have a general role in development. As a step in dissecting the biochemical mode of action of the COP9 signalosome, we determined the sequence of proteins that copurify with this complex. Here we describe the association between components of the COP9 signalosome (CSN1, CSN7, and CSN8) and two subunits of eukaryotic translation initiation factor 3 (eIF3), eIF3e (p48, known also as INT-6) and eIF3c (p105). To obtain a biochemical marker for Arabidopsis eIF3, we cloned the Arabidopsis ortholog of the eIF3 subunit eIF3b (PRT1). eIF3e coimmunoprecipitated with CSN7, and eIF3c coimmunoprecipitated with eIF3e, eIF3b, CSN8, and CSN1. eIF3e directly interacted with CSN7 and eIF3c. However, eIF3e and eIF3b cofractionated by gel filtration chromatography in a complex that was larger than the COP9 signalosome. Whereas eIF3, as detected through eIF3b, localized solely to the cytoplasm, eIF3e, like CSN7, was also found in the nucleus. This suggests that eIF3e and eIF3c are probably components of multiple complexes and that eIF3e and eIF3c associate with subunits of the COP9 signalosome, even though they are not components of the COP9 signalosome core complex. This interaction may allow for translational control by the COP9 signalosome.

Effect of ethanol on the production of carboxypeptidase Y using the GAL10 promoter in a Saccharomyces cerevisiae gal80 mutant

In the course of studying carboxypeptidase Y (CPY) production, we found that the expression level of the gene, which is under the control of the GAL10 promoter, increased in a Saccharomyces cerevisiae gal80 mutant grown in a medium containing ethanol as the sole carbon source. In the cultivation of the gal80 mutant KS58-2D/pCY303 carrying a multicopy plasmid, which contains the PRC1 gene fused to the GAL10 promoter, CPY production continued after the consumption of galactose. In this phase, the cells utilized ethanol as the carbon source. To increase the CPY production level, we examined the effect of carbon source feeding in a fed-batch culture. The production level in the fed-batch culture using ethanol was 1.3-fold higher than that in a batch culture and 1.6-fold higher than that in a fed-batch culture using galactose. By 5'-deletion analysis of the GAL10 promoter, the region between -256 and -232 was found to be important for the promoter activity in the gal80 mutant growing in the presence of ethanol.

Structure/functional properties of the yeast dual regulator protein NGG1 that are required for glucose repression

NGG1p/ADA3p is a yeast dual function regulator required for the complete glucose repression of GAL4p-activated genes (Brandl, C. J., Furlanetto, A. M., Martens, J. A., and Hamilton, K. S. (1993) EMBO J. 12, 5255-5265). Evidence for a direct role for NGG1p in regulating activator function is supported by the finding that NGG1p is also required for transcriptional activation by GAL4p-VPl6 and LexA-GCN4p (Pina, B., Berger, S. L., Marcus, G. A., Silverman, N., Agapite, J., and Guarente, L. (1993) Mol. Cell. Biol. 13, 5981-5989). By analyzing deletion derivatives of the 702-amino acid protein, we identified a region essential for glucose repression within residues 274-373. Essential sequences were further localized to a segment rich in Phe residues that is predicted to be an amphipathic alpha helix. As well as finding mutations within this region that reduced glucose repression, we identified mutations that made NGG1p a better repressor. In addition, NGG1p probably represses GAL4p activity as part of a complex containing ADA2p because single and double disruptions of ngg1 and ada2 had comparable effects on glucose repression. We also localized a transcriptional activation domain within the amino-terminal amino acids of NGG1p that is proximal or overlapping the region required for glucose repression. Activation by GAL4p-NGG1p(1-373) requires ADA2p; however, activation by GAL4p-NGG1p(1-308), is ADA2p-independent. This suggests that a site required for ADA2p interaction lies between amino acids 308 and 373 and that ADA2p has a regulatory role in activation by GAL4p-NGG1p(1-373).

Shared control of maltose induction and catabolite repression of the MAL structural genes in Saccharomyces

Maltose utilization in yeast requires the presence of any one of the five unlinked, homologous MAL loci. Transcription of the two structural genes MALT (permease) and MALS (maltase) is induced by maltose and catabolite-repressed by glucose. MAL6T and MAL6S share a common 5' intergenic sequence; deletion studies within this sequence revealed a bi-directionally functioning upstream activation sequence (UASM) consisting of four 11 bp homologous sites. Activation of these sites by the MALR protein results in the coordinate expression of MAL6T and MAL6S. The basal promoter activates MALS expression to a greater extent than MALT and is located in a region that overlaps UASM. Deletion of several subsites within the UASM has an asymmetric effect on MAL gene expression, having a greater affect on MALT than on MALS. Catabolite repression of MAL6T and MAL6S by glucose is controlled at several levels. Using disruption mutants, the positively acting MAL1R protein was also found to play a role in catabolite repression of MAL6T and MAL6S.

TSF1 to TSF6, required for silencing the Saccharomyces cerevisiae GAL genes, are global regulatory genes

The Saccharomyces cerevisiae GAL1 and GAL10 genes are controlled in response to the availability of galactose and glucose by multiple activating and repressing proteins bound at adjacent or overlapping sites in UASG. Negative control elements in UASG, designated GAL operators GALO1 to GALO6, are required to silence basal level transcription of GAL1 and GAL10 when galactose is absent. We isolated and characterized recessive mutations in six nuclear genes, TSF1 to TSF6, that impair silencing of GAL1 and GAL10 gene expression. Surprisingly, the results of several experiments suggest that the TSF genes encode global regulatory factors. tsf1 to tsf6 mutations derepressed expression from yeast CYC-GAL hybrid promoters (fused to lacZ) that harbor a variety of operator sequences, and caused pleiotropic defects in cell growth, mating, and sporulation. S1 mapping and Northern blot results for tsf3 suggest that the molecular defect is at the transcriptional level. Mutant phenotypes were additive in certain combinations of tsf double mutants, implying that more than one silencing pathway is involved in TSF1 to TSF6 function. Most significantly, mutations in all six TSF1 to TSF6 genes activated expression from GAL1 and CYC1 promoters (fused to lacZ) lacking upstream activating sequences. Combined, the simplest interpretation of these results is that TSF1 to TSF6 encode factors that control the function of the basic RNA polymerase II transcriptional machinery.

Specific binding sites in the alcR and alcA promoters of the ethanol regulon for the CREA repressor mediating carbon catabolite repression in Aspergillus nidulans

The CREA repressor responsible for carbon catabolite repression in Aspergillus nidulans represses the transcription of the ethanol regulon. The N-terminal part of the CREA protein encompassing the two zinc fingers (C2H2 class family) and an alanine-rich region was expressed in Escherichia coli as a fusion protein with glutathione-S-transferase. Our results show that CREA is a DNA-binding protein able to bind to the promoters of both the specific trans-acting gene, alcR, and of the structural gene, alcA, encoding the alcohol dehydrogenase I. DNase I protection footprinting experiments revealed several specific binding sites in the alcR and in the alcA promoters having the consensus sequence 5'-G/CPyGGGG-3'. The disruption of one of these CREA-binding sites in the alcR promoter overlapping the induction target for the trans-activator ALCR results in a partially derepressed alc phenotype and derepressed alcR transcription, showing that this binding site is functional in vivo. Our data suggest that CREA represses the ethanol regulon by a double lock mechanism repressing both the trans-acting gene, alcR, and the structural gene, alcA.