Physiological response of S. cerevisiae excess cysteine or cystine

Excess cysteine (and cystine) is known to be toxic in organisms. Due to the absence of cysteine dioxygenase (involved in degradation of excess cysteine in humans and pathogenic fungi) in non pathogenic fungi such as S. cerevisiae, mechanism of cysteine (and cystine) tolerance is yet to be addressed. In order to understand the physiological (transcriptional) response to excess cytosolic cysteine or cystine, S. cerevisiae (MET15 yct1Δ) cells constitutively expressing either cysteine (YCT1) or cystine specific transporter (C. glabrata CgCYN1) were exposed to excess cysteine or cystine (500µM) respectively for 5hrs and analysed with repect to the untreated respective controls for the transcriptional response.