Control of mitochondrial gene expression Nuclear encoded mitochondrial gene expression Mitochondrial encoded genes Must be coordinated All of the enzymes required for DNA replication And transcription are encoded in nucleus

Retrograde regulation - General term for mitochondrial signalling Defined as cellular responses to changes in functional state of mitochondria Anterograde regulation Defined as transfer of information and material from the nucleus (via cytoplasm) to mitochondria

Aerobic metabolism: (oxidative metabolism) Glycolysis TCA cycle oxidative phosphorylation Anaerobic metabolism: (fermentation) Glucose  Acetyl CoA  Ethanol Diauxic shift: Metabolic change as fermentable carbon source is used up from… Glucose Fermentative (Glycolysis  Ethanol) Oxidative Metabolism (Ethanol  TCA cycle) to… yeast carbon metabolism

NADH + CO 2 One pyruvate molecule is completely oxidised to CO 2 4-Carbons 3-Carbons CO 2 6-Carbons NADH + CO 2 NADH FADH Outline of Tricarboxylic Acid Cycle The NADH and FADH produced are oxidised by the respiratory electron transport chain

metabolic remodelling Metabolic pathways were altered in respiratory deficient cells Intermediates of TCA cycle needed for synthesis of amino acids and nucleotides Metabolic pathways altered:  OAA and Acetyl-CoA supply  Acetyl-CoA hydrolase  in enzymes involved in flux and conversion of metabolites made by fatty acid oxidation to TCA and glyoxylate cycle intermediates.  in nutrient and metabolite transporters.  in enzymes for reoxidation of NADH reconfigure metabolism by recruiting peroxisomal activities, small molecule transport systems and lipid, sugar and amino acid turnover to get more OAA and Acetyl-CoA.

CIT2 gene expression upregulated 50 fold Positive regulators =Rtg1, Rtg2 and Rtg3 Negative regulators = Mks1, Lst8p, Bmh1p, Bmh2p Rtg1 an Rtg3 - basic helix-loop-helix-leucine zipper (bhlh-Zip) transcription factors that heterodimerise and activate transcription of genes that contain an R Box -GTCAC Rtg2 acts upstream of Rtg1 and 3 sensor of mitochondrial dysfunction transducer of signals

Off state - Rtg1 and 3 sequestered in cytoplasm - Rtg 3 phosphorylated at multiple sites On state- Rtg3 becomes partially dephosphorylayed - enters nucleus (with Rtg1) to activate transcription of genes with an R box Thus it is the location that controls activity Note in mutants lacking Rtg2 the retrograde response is completely lost indicating that Rtg2 plays a crucial role in activating Rtg1 and 3

Regulators of Rtg2 Genetic screens to identify Mks1p - negative regulator - Absence means CIT2 expression constitutively high - Phosphoprotein Retrograde pathway on - Mks1p is largely dephosphorylated In a complex with Rtg2. Retrograde pathway off - Mks1p is highly phosphoryalyed and not bound to Rtg2, but to proteins Bmh1p and Bmh2p - as yet not known how this complex negatively regulates

Lst8p - negative regulator of retrograde response - Acts at two points upstream of Rtg2 downstream of Rtg2 Shown by the fact two classes of mutants exists for Lst8p - class I cannot bypass need for Rtg2 = upstream -class II - no need for Rtg2 = downstream

TOR signalling in yeast (target for rapamycin) growth control nutrient signalling RTG pathway activated when TOR signalling is inactivated Lst8p is an integral component of Tor1 and 2 complexes Acts as a positive regulator in these complexes Details not yet clear on interaction of TOR and RTG pathway but thought to be indirect as RTG response still takes place if TOR pathway active

Retrograde response in mammalian cells