Yeast adenylate kinase is transcribed constitutively from a promoter in the short intergenic region to the histone H2A-1 gene.

Yeast mitochondrial adenylate kinase (high molecular mass form, gene locus: AKY2) is encoded on chromosome IV of the same DNA strand as histone H2A-1. The nontranslated intergenic region spans 560 bp, the nontranscribed spacer can be estimated to comprise at most 300 bp. The TATA-box sequence is contained in a striking environment consisting of 20 alternating pyrimidines and purines. The AKY2 transcript is made constitutively: (i) the cellular mRNA concentration does not vary significantly with either growth conditions or elapse of the cell cycle; (ii) beta-galactosidase activity is about constant in yeast cells grown on various carbon sources after transformation with AKY2-promoter/lacZ fusions; (iii) primer elongation analysis shows that utilization of 5 initiation sites is qualitatively and quantitatively independent of the growth conditions and the carbon source used; (iv) Western blot analysis and adenylate kinase activity measurements indicate the absence of post-transcriptional controls as well.

Oxaloacetate and malate transport by plant mitochondria.

The permeability of mitochondria from pea (Pisum sativum L. var Kleine Rheinländerin) leaves, etiolated pea shoots, and potato (Solanum tuberosum) tuber for malate, oxaloacetate, and other dicarboxylates was investigated by measurement of mitochondrial swelling in isoosmolar solutions of the above mentioned metabolites. For the sake of comparison, parallel experiments were also performed with rat liver mitochondria. Unlike the mammalian mitochondria, the plant mitochondria showed only little swelling in ammonium malate plus phosphate media but a dramatic increase of swelling on the addition of valinomycin. Similar results were obtained with oxaloacetate, maleate, fumarate, succinate, and malonate. n-Butylmalonate and phenylsuccinate, impermeant inhibitors of malate transport in mammalian mitochondria, had no marked inhibitory effect on valinomycin-dependent malate and oxaloacetate uptake of the plant mitochondria. The swelling of plant mitochondria in malate plus valinomycin was strongly inhibited by oxaloacetate, at a concentration ratio of oxaloacetate/malate of 10(-3). From these findings it is concluded: (a) In a malate-oxaloacetate shuttle transferring redox equivalents from the mitochondrial matrix to the cytosol, malate and oxaloacetate are each transported by electrogenic uniport, probably linked to each other for the sake of charge compensation. (b) The transport of malate between the mitochondrial matrix and the cytosol is controlled by the oxaloacetate level in such a way that a redox gradient can be maintained between the NADH/NAD systems in the matrix and the cytosol. (c) The malate-oxaloacetate shuttle functions mainly in the export of malate from the mitochondria, whereas the import of malate as a respiratory substrate may proceed by the classical malate-phosphate antiport.

Yeast adenylate kinase is active simultaneously in mitochondria and cytoplasm and is required for non-fermentative growth.

Displacement of the single copy structural gene for yeast adenylate kinase (long version) by a disrupted nonfunctional allele is tolerated in haploid cells. Since adenylate kinase activity is a pre-requisite for cell viability, the survival of haploid disruption mutants is indicative of the presence of an adenylate kinase isozyme in yeast, capable of forming ADP from AMP and, thus, of complementing the disrupted allele. The phenotype of these disruption mutants is pet, showing that complementation occurs only under fermentative conditions. Even on glucose, growth of the disruption mutants is slow. Adenylate kinase activity is found both in mitochondria and cytoplasm of wild type yeast. The disruption completely destroys the activity in mitochondria, whereas in the cytoplasmic fraction about 10% is retained. An antibody raised against yeast mitochondrial adenylate kinase recognizes cross-reacting material both in mitochondria and cytoplasm of the wild type, but fails to do so in each of the respective mutant fractions. The data indicate that yeast adenylate kinase (long version, AKY2) simultaneously occurs and is active in mitochondria and cytoplasm of the wild type. Nevertheless, it lacks a cleavable pre-sequence for import into mitochondria. A second, minor isozyme, encoded by a separate gene, is present exclusively in the cytoplasm.