Figure 4

Amino acid addition to a medium containing poor nitrogen source rescues DEP toxicity. (A) SPS pathway. When amino acids are absent, SPS pathway remains inactive. Ssy5 remains inactive and does not cleave the pro-domain of Stp1, preventing the transcription of amino acid permease (AAP) genes. When amino acids are present, SPS pathway is active. Upon binding to the amino acid sensor Ssy1, Ssy5 is activated and cleaves the pro-domain of Stp1, permitting it to enter the nucleus and associate with Dal81 to induce transcription of amino acid permease (AAP) genes. (B) Growth inhibition of WT, gap1Δ and gap1Δ ssy1Δ (Σ1278b background) in minimal urea media with no amino acids or with 5 mM ammonium sulfate or phenylalanine, or leucine. Error bars indicate standard deviation (N = 2). Each consecutive bar represents a doubled concentration of the preceding bar, with 25 mM as the maximal concentration used for DEP.