High impact information on MET4

• The critical target of SCF(Met30) is the transcription factor Met4, as deletion of MET4 suppresses the lethality of met30 mutants [1].
• However, transcriptional repression of Met4 target genes correlates with Cdc34/SCF(Met30)-dependent ubiquitination of Met4 [1].
• In yeast, the activator Met4 is inhibited by the SCF(Met30) ubiquitin ligase, which recognizes and oligo-ubiquitylates Met4 [2].
• In the latter growth condition, oligo-ubiquitylated Met4 is not recruited to MET gene promoters, but is recruited to the SAM genes, which are required for production of S-adenosylmethionine, an unstable metabolite that is not present in rich medium [2].
• Here, we demonstrate that in minimal media, Met4 is ubiquitylated and rapidly degraded in response to methionine excess, whereas in rich media, Met4 is oligo-ubiquitylated but remains stable [2].

Biological context of MET4

• MET4, a leucine zipper protein, and centromere-binding factor 1 are both required for transcriptional activation of sulfur metabolism in Saccharomyces cerevisiae [3].
• The presence of consensus sequences for other potential regulatory elements in the MET4 promoter suggests a complex regulation of this gene [4].
• Disruption of MET4 resulted in methionine auxotrophy with no other phenotype [4].
• Linkage to MET4 would place the LEU4 gene on the left arm of chromosome XIV [5].
• Results from standard meiotic mapping experiments indicate that TOP2 is about 16 centi-Morgans to the centromere proximal side of MET4 [6].

Associations of MET4 with chemical compounds

• When the level of intracellular AdoMet increases, the transcription activation function of Met4 is prevented by Met30p, which binds to the Met4 inhibitory region [7].
• The data suggest that azoxybacilin acts on at least two steps in the expression of sulfite reductase; the transcriptional activation of MET4 and a posttranscriptional regulation in MET10 expression [8].
• Coupling of the transcriptional regulation of glutathione biosynthesis to the availability of glutathione and methionine via the Met4 and Yap1 transcription factors [9].
• Moreover, the deletion of MET4 leads to increased acetaldehyde sensitivity [10].
• The main transcriptional activator of the sulfate assimilation pathway, Met4p, plays an essential role in this sulfur-sparing response [11].

Physical interactions of MET4

• GCN4 binding sequences are present between the divergently transcribed MET4 and LEU4 genes [4].
• Cbf1 belongs to the basic helix-loop-helix DNA-binding protein family while Met4 and Met28 are two basic leucine zipper (bZIP) factors [12].
• Here we show that a single ubiquitin chain is attached to Met4 through lysine at position 163 [13].
• By the two-hybrid method, we showed that Met30p interacts with Met4p and identified a region of Met4p involved in this interaction [14].

Regulatory relationships of MET4

• Over-expression of MET4 resulted in leaky expression from the otherwise tightly regulated MET3 promoter under its control [4].
• Transcriptional studies showed that MET4 was regulated by the general amino acid control and hence by another bZIP protein encoded by GCN4 [4].
• The requirement for Met4 in regulating GSH1 expression is lost in the absence of the centromere-binding protein Cbf1 [9].

Other interactions of MET4

• In this paper, we demonstrate that other pathways are used to recruit Met4p on the 5' upstream region of the two genes, MET3 and MET28 [15].
• The obtained results suggest that the binding of CBF1 to its cognate sequences increases the ability of MET4 to stimulate transcription of the MET genes [3].
• A mutation in the MET4 gene abolishes transcription of both genes MET16 and MET25 [16].
• The use of LexA-MET4 fusion proteins also reveals that the leucine zipper of MET4 is required for the recognition of the MET25 promoter [3].
• Furthermore, yeast cells exposed to the xenobiotic 1-chloro-2,4-dintrobenzene are rapidly depleted of glutathione, accumulate oxidized thioredoxins, and elicit the Yap1/Met4-dependent transcriptional response of GSH1 [9].
• We further demonstrated that Met32 is part of the Cbf1-Met4 complex bound to Cbf1-recruiting promoter elements and that Met31/32 are required for formation of a stable Met4-Cbf1 transcription complex [17].

Analytical, diagnostic and therapeutic context of MET4

• Complementation tests and genetic analysis demonstrated that the affected gene was MET4 [5].
• By using mobility shift assays, we report here that the in vitro reconstitution of the Cbf1-Met4-Met28 complex on MET16UAS can be obtained with purified recombinant proteins [12].

References