S. cerevisiae Lys20p and Lys21p

In the yeast Saccharomyces cerevisiae, AAA or alpha-amino adipate pathway is responsible for lysine biosynthesis wherein the first committed step involves condensation of acetyl CoA (AcCoA) with alpha-ketoglutarate (alpha-KG) to generate homocitrate as well as CoA in the nucleus, and this reaction is catalyzed by the homocitrate synthase isozymes encoded by LYS20 and LYS21 which belongs to alpha-IPM synthase/homocitrate synthase family and are 92% identical in amino acid sequence. Expression of both LYS20 and LYS21 is upregulated through Gcn4p upon amino acid deprivation, and their positive regulation is also facilitated by Lys14p (transcriptional activator from Zn-Cys cluster family) with co-inducer alpha-AASA (2-aminoadipate semialdehyde). Moreover, LYS20 and LYS21 are positively co-regulated by target of rapamycin or TOR signalling pathway coupled with protein kinase A, through a LYS14-GCN4-independent pathway. Therefore, LYS20 and LYS21 plays a key role in maintaining levels of lysine, an amino acid preferentially located in the vacuole, therefore not available as a source of nitrogen or carbon source, and lysine has been sown to play important physiological roles: contributing to the build-up of H2O2 triggered stress response, prevention of apoptosis induced upon amino acid starvation, and cryoprotection.

Full Name

Saccharomyces cerevisiae Lys20p and Lys21p