The copper-sensing transcription factor Mac1, the histone deacetylase Hst1, and nicotinic acid regulate NAD biosynthesis in budding yeast.

NADH (NAD) is an essential metabolite involved in various cellular biochemical processes. The regulation of NAD metabolism is incompletely understood. Here, using budding yeast (), we established an NAD intermediate-specific genetic system to identify factors that regulate the branch of NAD biosynthesis. We found that a mutant strain (Δ) lacking Mac1, a copper-sensing transcription factor that activates copper transport genes during copper deprivation, exhibits increases in quinolinic acid (QA) production and NAD levels. Similar phenotypes were also observed in the Δ strain, deficient in the NAD-dependent histone deacetylase Hst1, which inhibits NAD synthesis by repressing gene expression when NAD is abundant. Interestingly, the Δ and Δ mutants shared a similar NAD metabolism-related gene expression profile, and deleting either or de-repressed the genes. ChIP experiments with the promoter indicated that Mac1 works with Hst1-containing repressor complexes to silence expression. The connection of Mac1 and expression suggested that copper stress affects NAD synthesis, and we show that copper stress induces both expression and QA production. Moreover, nicotinic acid inhibited NAD synthesis through Hst1-mediated repression, hindered the reuptake of extracellular QA, and thereby reduced NAD synthesis. In summary, we have identified and characterized novel NAD homeostasis factors. These findings will expand our understanding of the molecular basis and regulation of NAD metabolism.