3 years ago

Diversification of Transcriptional Regulation Determines Subfunctionalization of Paralogous Branched Chain Aminotransferases in the Yeast Saccharomyces cerevisiae.

Saccharomyces cerevisiae harbors BAT1 and BAT2 paralogous genes encoding branched chain aminotransferases (BCATs), showing opposed expression profiles and physiological role. Accordingly, in primary nitrogen sources such as glutamine, BAT1 expression is induced, supporting Bat1-dependent valine-isoleucine-leucine (VIL) biosynthesis, while BAT2 expression is repressed. Conversely, in the presence of VIL as sole nitrogen source, BAT1 expression is hindered while that of BAT2 is activated resulting in Bat2-dependent VIL catabolism. Presented results confirm that BAT1 expression is determined by transcriptional activation through the action of the Leu3-α-IPM active isoform, and uncovers the existence of a novel α-IPM biosynthetic pathway operating in a put3Δ mutant grown on VIL, through Bat2-Leu2-Leu1 consecutive action. The classic α-IPM biosynthetic route operates in glutamine through the action of the leucine sensitive α-isopropylmalate synthases (α-IPMS). Presented results also show that BAT2 repression in glutamine can be alleviated in an ure2Δ mutant or through Gcn4-dependent transcriptional activation. Thus, when S. cerevisiae is grown on glutamine, VIL biosynthesis is predominant and is preferentially achieved through BAT1, while on VIL as sole nitrogen source, catabolism prevails and is mainly afforded by BAT2.

Publisher URL: http://doi.org/10.1534/genetics.117.300290

DOI: 10.1534/genetics.117.300290

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