SUMMARY PARAGRAPH for LEU1
LEU1 encodes isopropylmalate isomerase (isopropylmalate dehydratase), which catalyzes the conversion of alpha-isopropylmalate into beta-isopropylmalate in the second step of leucine biosynthesis (see pathway diagram) (3 and reviewed in 4). Leu1p is an iron-sulfur (Fe-S) protein that is very sensitive to degradation when removed from intact cells but can be stabilized by high glycerol or high ionic concentrations, conditions which also inactivate the enzyme (5). In contrast to most of the enzymes involved in the superpathway of branched-chain amino acid (valine, leucine, isoleucine) biosynthesis, which are mitochondrial, Leu1p localizes to the cytoplasm (6).
Like the other genes in the leucine biosynthesis pathway, LEU1 is transcriptionally repressed in the presence of leucine (7, 1). LEU1 expression is induced by the transcriptional regulator Leu3p bound to the leucine precursor alpha-isopropylmalate, which recognizes an upstream activation signal in the LEU1 promoter (8, 9). LEU1 transcription has also been shown to be upregulated by the transcriptional activator Gcn4p (10).
leu1 null mutations result in leucine auxotrophy (1), as do mutations affecting gene products that contribute to the incorporation or stability of the Leu1p Fe-S cluster, such as Atm1p and Sod1p (11 and reviewed in 4).
Last updated: 2006-08-08