Signalling between mitochondria and the nucleus regulates the expression of a new D-lactate dehydrogenase activity in yeast

We have adapted a LacZ promoter trap screen developed by Burns et al. (1994 ) to search for genes whose expression is dependent on Rtg2p, a protein wit h an N-terminal hsp70/actin/sugar kinase ATP binding domain. Rtg2p acts ups tream of the basic helix-loop-helix/leucine zipper transcription factors, R tg1p and Rtg3p. All three proteins are known to be required for the express ion of the CIT2 gene, which encodes a peroxisomal isoform of citrate syntha se whose expression is also dependent on the functional state of mitochondr ia. Using this screen, we have identified a previously uncharacterized gene , YEL071w, predicted to encode a protein of 496 amino acids that shares 80% homology and 60% sequence identity with actin interacting protein 2, encod ed by the AIP2 gene; both proteins also share sequence similarity to a D-la ctate dehydrogenase encoded by the DLD1 gene. Expression of YEL071w is depe ndent on the functional state of mitochondria and on all three of the Rtg p roteins, whereas AIP2 expression is independent of the Rtg proteins and the functional state of mitochondria. Like CIT2, the 5' flanking region of YEL 071w contains two R box binding sites for the Rtg1p/Rtg3p heterodimeric tra nscription complex. Both R boxes are necessary for full YEL071w expression. We show that YEL071w and AIP2 encode proteins with D-lactate dehydrogenase activity, the former located in the cytoplasm and the latter in the mitoch ondrial matrix. Our data thus provide gene assignments for two previously u nrecognized D-lactate dehydrogenase activities in yeast. Copyright (C) 1999 John Wiley & Sons, Ltd.