Cys6

Cys6 is a transcription factor in the budding yeast Saccharomyces cerevisiae. It belongs to the Zn2Cys6 binuclear cluster family and is encoded by the CYS6 gene. Cys6 regulates the expression of genes involved in sulfate uptake and sulfur assimilation, enabling the biosynthesis of the sulfur-containing amino acids cysteine and methionine. Its activity is essential for growth under conditions where inorganic sulfur must be acquired and assimilated.

Structurally, Cys6 contains the characteristic Zn2Cys6 DNA-binding domain at the N-terminus, followed by regulatory regions and a C-terminal activation domain. The DNA-binding domain recognizes promoter elements that typically contain CGG core motifs, a common feature of Zn2Cys6 transcription factors. This enables Cys6 to bind promoters of its target genes and recruit the transcriptional machinery to initiate transcription.

Regulation of Cys6 is closely tied to the cell’s sulfur status. Under sulfur limitation, Cys6 localizes to the nucleus and activates a broad regulon of genes involved in sulfate transport and sulfur assimilation, facilitating production of essential sulfur-containing compounds. When sulfur is abundant, Cys6 activity is downregulated to conserve resources. Its function is coordinated with other regulators of sulfur metabolism through protein–protein interactions that modulate transcriptional output.

Impact of CYS6 disruption includes impaired induction of sulfur metabolism genes and reduced growth on media requiring sulfate assimilation, along with altered intracellular levels of cysteine and methionine. As a well-characterized example of Zn2Cys6 transcription factors in fungi, Cys6 provides a model for studying transcriptional regulation and fungal sulfur metabolism.