Submitochondrial localization, cell-free synthesis, and mitochondrial import of 2-isopropylmalate synthase of yeast.

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Abstract
2-Isopropylmalate synthase (EC 4.1.3.12) of yeast is a mitochondrial enzyme. Evidently, a large part of the 2-isopropylmalate synthase activity that is associated with the mitochondria is located in the mitochondrial matrix. In vitro translation of total yeast RNA followed by immunoprecipitation with anti-2-isopropylmalate synthase antibody yields 2 polypeptides. The larger of these has an apparent MW identical to that of purified 2-isopropylmalate synthase subunit (.apprx. 65,000). It is incorporated into isolated yeast mitochondria with no detectable change in MW. The import requires energy. The smaller polypeptide migrates to a position corresponding to a MW of 63,000-64,000. It is not taken up by mitochondria. Both polypeptides, which also can be obtained by immunoprecipitation of crude extracts, become labeled when in vitro translation is performed in the presence of N-formyl[35S]methionyl-tRNAf. Mutants with no detectable 2-isopropylmalate synthase activity are deficient in either one or both synthase-related polypeptides. Recent evidence for 2 2-isopropylmalate synthase-encoding genes in yeast is discussed.

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