RTG Genes in Yeast That Function in Communication between Mitochondria and the Nucleus Are Also Required for Expression of Genes Encoding Peroxisomal Proteins

Abstract

In Saccharomyces cerevisiae cells with dysfunctional mitochondria, such as in petites, the CIT2 gene encoding the peroxisomal glyoxylate cycle enzyme, citrate synthase 2 (CS2), is transcriptionally activated by as much as 30-fold, a phenomenon we call retrograde regulation. Two genes, RTG1 and RTG2, are required for both basal and elevated expression of CIT2 (Liao, X., and Butow, R. A.(1993) Cell 72, 61-71). Different blocks in the tricarboxylic acid cycle also elicit an increase in CIT2 expression, but not to the extent observed in petites. We have examined whether other genes of the glyoxylate cycle exhibit retrograde regulation and the role of RTG1 and RTG2 in their expression. Of the glyoxylate cycle genes tested, CIT2 is the only one that shows retrograde regulation, suggesting that CS2 may be an important control point for metabolic cross-feeding from the glyoxylate cycle to mitochondria. Surprisingly, RTG1 and RTG2 are required for efficient growth of cells on medium containing oleic acid, a condition which induces peroxisome biogenesis; these genes are also required together for oleic acid induction of three peroxisomal protein genes tested, POX1 and CTA1 involved β-oxidation of long chain fatty acids and PMP27, which encodes the most abundant protein of peroxisomal membranes. These data indicate that, in addition to their role in retrograde regulation of CIT2, the RTG genes are important for expression of genes encoding peroxisomal proteins and are thus key components in a novel, three-way path of communication between mitochondria, the nucleus, and peroxisomes. In Saccharomyces cerevisiae cells with dysfunctional mitochondria, such as in petites, the CIT2 gene encoding the peroxisomal glyoxylate cycle enzyme, citrate synthase 2 (CS2), is transcriptionally activated by as much as 30-fold, a phenomenon we call retrograde regulation. Two genes, RTG1 and RTG2, are required for both basal and elevated expression of CIT2 (Liao, X., and Butow, R. A.(1993) Cell 72, 61-71). Different blocks in the tricarboxylic acid cycle also elicit an increase in CIT2 expression, but not to the extent observed in petites. We have examined whether other genes of the glyoxylate cycle exhibit retrograde regulation and the role of RTG1 and RTG2 in their expression. Of the glyoxylate cycle genes tested, CIT2 is the only one that shows retrograde regulation, suggesting that CS2 may be an important control point for metabolic cross-feeding from the glyoxylate cycle to mitochondria. Surprisingly, RTG1 and RTG2 are required for efficient growth of cells on medium containing oleic acid, a condition which induces peroxisome biogenesis; these genes are also required together for oleic acid induction of three peroxisomal protein genes tested, POX1 and CTA1 involved β-oxidation of long chain fatty acids and PMP27, which encodes the most abundant protein of peroxisomal membranes. These data indicate that, in addition to their role in retrograde regulation of CIT2, the RTG genes are important for expression of genes encoding peroxisomal proteins and are thus key components in a novel, three-way path of communication between mitochondria, the nucleus, and peroxisomes. It has recently become clear that alterations in the functional state of mitochondria and chloroplasts can result in changes in nuclear gene expression(1Susek R.E. Ausubel F.M. Chory J. Cell. 1993; 74: 787-799Google Scholar, 2Susek R.E. Chory J. Aust. J. Plant Physiol. 1992; 19: 387-399Google Scholar, 3Mayfield S.P. Curr. Opin. Cell Biol. 1990; 2: 509-512Google Scholar, 4Parikh V.S. Morgan M.M. Scott R. Clements L.S. Butow R.A. Science. 1987; 235: 576-580Google Scholar, 5Liao X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar, 6Liao X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar, 7Lunardi J. Attardi G. J. Biol. Chem. 1991; 266: 16534-16540Google Scholar, 8Fearon K. Mason T.L. Mol. Cell. Biol. 1988; 8: 3636-3646Google Scholar, 9Conrad-Webb H. Butow R.A. Mol. Cell. Biol. 1995; 15: 2420-2428Google Scholar). We have called this pathway of interorganelle communication retrograde regulation and suggested that it is a mechanism for the cell to adjust to changes in mitochondrial or chloroplast activities(10Shyjan A.W. Butow R.A. Current Biol. 1993; 3: 398-400Google Scholar). One example in yeast that supports the idea that retrograde regulation is an adaptive process to changes in mitochondrial function is the dramatic elevation in expression of the CIT2 gene in cells with altered mitochondrial activity(5Liao X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar). CIT2 is a nuclear gene encoding the glyoxylate cycle isoform of citrate synthase (CS2)(11Rosenkrantz M. Alam T. Kim K.-S. Clark B.J. Srere P.A. Guarente L.P. Mol. Cell. Biol. 1986; 6: 4509-4515Google Scholar); that enzyme, together with other enzymes of the glyoxylate cycle, is located in peroxisomes of Saccharomyces cerevisiae(12Lewin A.S. Hines V. Small G.M. Mol. Cell. Biol. 1990; 10: 1399-1405Google Scholar, 13McCammon M.T. Veenhuis M. Trapp S.B. Goodman J.M. J. Bacteriol. 1990; 172: 5816-5827Google Scholar). CIT2 expression is increased 5-10 fold in cells in which the tricarboxylic acid cycle is blocked because of a disruption of CIT1, the gene encoding the mitochondrial isoform of citrate synthase, CS1(14Suissa M. Suda K. Schatz G. EMBO J. 1984; 3: 1773-1781Google Scholar). This increase in CIT2 expression compensates for the loss of CS1 activity through metabolic cross-feeding between the glyoxylate and tricarboxylic acid cycles(5Liao X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar). The greatest increase in CIT2 expression we have observed is in respiratory-deficient ρ0 petites, which lack mitochondrial DNA. In those cells, the CIT2 mRNA abundance is as much as 30-fold greater than in their isochromosomal respiratory-competent (ρ+) counterparts. The increased abundance of CIT2 mRNA in cells with dysfunctional mitochondria is due to transcriptional activation and is mediated in cis through an upstream activation site (UASr) in the 5’ flanking region of the gene(5Liao X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar, 6Liao X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). We previously reported that transcriptional regulation of CIT2 requires at least two trans acting factors encoded by the single copy nuclear genes, RTG1 and RTG2(6Liao X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). RTG1 encodes a basic helix-loop-helix transcription factor that binds to the CIT2 UASr, while RTG2 encodes a protein of unknown function that probably acts indirectly in the transactivation of CIT2 expression. A recent report shows that the deduced sequence of the RTG2-encoded protein has an ATP binding domain with similarity to bacterial enzymes that hydrolyze the transcriptional regulators, ppGpp and pppGpp(15Koonin E.V. Trends Biochem. Sci. 1994; 19: 156-157Google Scholar). We have recently identified a third gene (RTG3) required for CIT2 expression1 1Y. Jia, J. Etheredge, B. Rothermel, and R. A. Butow, unpublished results. 1Y. Jia, J. Etheredge, B. Rothermel, and R. A. Butow, unpublished results. whose properties will be reported elsewhere. The products of both RTG1 and RTG2 are required not only for the elevated expression of CIT2 in cells with dysfunctional mitochondria but also for its basal expression in otherwise wild-type cells. Although neither RTG1 nor RTG2 are essential genes, cells with mutant alleles of either are glutamate-aspartate auxotrophs and are unable to grow on acetate as a sole carbon source. These growth requirements are characteristic of cells with blocks in both the tricarboxylic acid and glyoxylate cycles, suggesting that the RTG genes play a role in the regulation of both(11Rosenkrantz M. Alam T. Kim K.-S. Clark B.J. Srere P.A. Guarente L.P. Mol. Cell. Biol. 1986; 6: 4509-4515Google Scholar). As yet, we have not found any significant lesions in enzymes of either cycle, other than the expected absence of CS2 activity and a reduction (~50%) in CS1 activity, which could account in any simple way for the rtg mutant phenotypes(16Small W.C. Brodeur R.D. Sandor A. Fedorova N. Li G. Butow R.A. Srere P.A. Biochemistry. 1995; 34: 5569-5576Google Scholar). These findings raise a number of questions regarding retrograde regulation and other possible functions of the RTG genes. For example, do tricarboxylic acid cycle blocks, other than a loss of CS1 activity, result in elevated CIT2 expression? Are other genes encoding glyoxylate cycle enzymes subject to retrograde regulation? And what role, if any, do the RTG genes play in expression of other peroxisomal proteins? This latter issue can be conveniently studied in yeast by growing cells in medium containing oleic acid. Under these conditions, there is a large induction of peroxisomal enzymes of the β-oxidation pathway accompanied by a general increase in the number of peroxisomes within the cell(17Kunau W.-H. Bhne S. del la Garza M. Kionka C. Mateblowski M. Schultz-Borchard U. Thieringer R. Biochem. Soc. Trans. 1988; 16: 418-420Google Scholar, 18Veenhuis M. Mateblowski M. Kunau W. Harder W. Yeast. 1987; 3: 77-84Google Scholar, 19Skoneczny S. Chelstowska A. Rytka J. Eur. J. Biochem. 1988; 174: 297-302Google Scholar). Here we show that a tricarboxylic acid cycle block caused by a disruption of MDH1 (encoding the tricarboxylic acid cycle isoform of malate dehydrogenase) elicits an elevation of CIT2 expression similar to that observed in cells with a disruption of CIT1. We show further that CIT2 is the only gene encoding a glyoxylate cycle enzyme among three others tested that is subject to significant retrograde regulation when its expression is compared between isochromosomal ρ+ and ρ0 cells. Finally, we show that RTG1 and RTG2 are required for full induction of expression of genes encoding other peroxisomal proteins, including an abundant protein associated with peroxisomal membranes whose synthesis follows peroxisome biogenesis (20Marshall P.A. Krimkevich Y.I. Lark R.H. Dyer J.M. Veenhuis M. Goodman J.M. J. Cell Biol. 1995; 129: 345-355Google Scholar, 21Erdman R. Blobel G. J. Cell Biol. 1995; 128: 509-523Google Scholar) when cells are grown in medium containing oleic acid. Thus, the RTG genes function not only in communication between mitochondria and the nucleus, but are likely to be involved in the oleic acid induction of peroxisome biogenesis as well. Yeast strains used in this study were COP161U7 (MATa, ade1 lys1 ura3 ρ+) and ethidium bromide-induced (see below) ρ0 isolates. Derivatives of ρ+ and ρ0 isolates were made containing URA3 insertion mutations in RTG1 (Δrtg1), RTG2 (Δrtg2), or in both chromosomal loci (Δrtg1 Δrtg2) as described by Liao and Butow(6Liao X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). Strain PSY142 (MATα, leu2 lys2, ura3 ρ+) and its cit1 disruption derivative (cit1::LEU2) was kindly provided by a disruption of MDH1 in used chain were made containing to MDH1 sequence from to at the 5’ of a gene and from to at the of the Biochemistry. 1988; Scholar); the of site for and The was the of A of MDH1 was by a containing the URA3 gene 5’ with The was from the and used to ρ+ PSY142 by a Curr. 1992; Scholar). The disruption was by ρ0 of these strains were by growing cells to in medium yeast and with ethidium The cells were and grown in the medium to were by for the loss of mitochondrial DNA. chain Yeast strains were grown at on medium yeast and with medium For oleic acid induction oleic acid was to the medium at a of while to an For most cells were by at of at an between and yeast was from of as described by 1990; Scholar). was and at For of mRNA of was on a containing by for at The were to a by in and to the were to the was for at were and for at for were by the the or by a was used for were in 2 and in at and in or on For to of were on to the were the of whose abundance not with growth or among the V.S. Morgan M.M. Scott R. Clements L.S. Butow R.A. Science. 1987; 235: 576-580Google with a for the of mRNA abundance of the genes in this study by B. Biochem. Scholar) the from R. J. Sci. U. S. A. Scholar); CIT2 (CS2), from X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar); CTA1 containing the and both and G. W. H. Eur. J. Biochem. 1988; Scholar); from (20Marshall P.A. Krimkevich Y.I. Lark R.H. Dyer J.M. Veenhuis M. Goodman J.M. J. Cell Biol. 1995; 129: 345-355Google Scholar) containing of sequence and of region of MDH1 sequence with flanking from to Biochemistry. 1988; Scholar); from to J. Biol. Chem. 1992; Scholar); from to R. Eur. J. Biochem. 1992; Scholar); synthase from to A. M.M. T. 1992; Scholar); POX1 from to A. R. 1990; Scholar). For these of yeast as described in in Yeast was used as a in used in were products were a with the were at 2 at and 2 at products were in and a The products were used as a in by or as The of CIT2 gene expression to dysfunctional mitochondria is observed in a of the abundance of CIT2 mRNA in ρ0 cells. In a of from ρ+ and ρ0 cells of CIT2 mRNA is abundant in the ρ0 derivative compared with ρ+ cells and when both strains are grown on A in mitochondrial function can also result in an increase in CIT2 for example, in ρ+ cells that have a disruption of the As in and CIT2 mRNA abundance is greater in cells than in the One to account for this increase in CIT2 expression is that it is a to the absence of any mitochondrial CS1 activity, a the metabolic cross-feeding of citrate in the glyoxylate cycle from peroxisomes to Biochem. Scholar). this we have CIT2 mRNA in ρ+ cells with a in the tricarboxylic acid cycle by a disruption of the gene encoding the mitochondrial isoform of malate Biochemistry. 1988; Scholar). As in and ρ+ cells with an MDH1 disruption also have elevated of CIT2 which in this is greater than the wild-type ρ+ This result the that increased expression of CIT2 is the result of a in the tricarboxylic acid cycle the The that the abundance of CIT2 mRNA is greater in lack an chain and than in ρ+ cells which lack tricarboxylic acid cycle activity that lesions in mitochondrial function may account for the of CIT2 expression in petites. This is with a that the abundance of CIT2 mRNA in ρ+ cells with a disruption can be further increased to the observed in if the cells are grown in the of the chain X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar). these findings indicate that in CIT2 expression can be probably by a of blocks in mitochondrial the metabolic between the glyoxylate and tricarboxylic acid Biochem. a key is whether the expression of other glyoxylate cycle genes CIT2 to the functional state of mitochondria. we have compared the mRNA in ρ+ and ρ0 of COP161U7 for three glyoxylate cycle genes, and of from these cells were with for of these genes as described and in the to The of these show that of these genes, only CIT2 is subject to significant retrograde regulation. In this the CIT2 mRNA abundance is greater in the ρ0 than in ρ+ cells, the mRNA for and are greater than The used for which is a by from the region of the gene (see to two neither of which shows a retrograde Thus, at this of not glyoxylate cycle genes are subject to retrograde regulation. RTG1 and RTG2 are required for both basal expression of CIT2 in wild-type cells and for its elevated expression in cells with dysfunctional X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). A of cells with mutant alleles of RTG1 or RTG2 is that are unable to acetate as a sole carbon source. is associated with block in the tricarboxylic acid cycle and is not observed in cells which lack only CS2 X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar, M. Alam T. Kim K.-S. Clark B.J. Srere P.A. Guarente L.P. Mol. Cell. Biol. 1986; 6: 4509-4515Google Scholar). These the of whether cells with mutant alleles of RTG1 and RTG2 could the two carbon by β-oxidation of fatty we whether ρ+ COP161U7 cells with alleles of RTG1 or RTG2 or both could grow on medium containing oleic acid as the sole carbon source. wild-type ρ+ and the mutant were on medium containing oleic acid and As a the were on shows that while strains grow on of the rtg mutant strains show growth on oleic acid medium compared with the wild-type A of the that growth for the and mutant is than the mutant The of the rtg mutant cells to oleic acid in the growth medium could be due to an in the induction of peroxisomal enzymes of the β-oxidation this we have to the of alleles of RTG1 and RTG2, both and in on the mRNA for three peroxisomal proteins to be in cells grown on oleic M. Mateblowski M. Kunau W. Harder W. Yeast. 1987; 3: 77-84Google Scholar, 19Skoneczny S. Chelstowska A. Rytka J. Eur. J. Biochem. 1988; 174: 297-302Google Scholar). These are and A by the POX1 and CTA1 genes, and a peroxisomal by the whose abundance in cells follows peroxisomal and is required for peroxisome and P.A. Krimkevich Y.I. Lark R.H. Dyer J.M. Veenhuis M. Goodman J.M. J. Cell Biol. 1995; 129: 345-355Google Scholar, 21Erdman R. Blobel G. J. Cell Biol. 1995; 128: 509-523Google Scholar). wild-type ρ+ cells from COP161U7 and the and mutant were grown on medium in the or absence of oleic acid. Under these conditions, of the strains will and the of oleic acid in the medium enzymes of the β-oxidation The of and were by of from these cells for (see A of the of these for a is in as growth of wild-type cells in the of oleic acid in a large increase in the abundance of the for three of these peroxisomal to wild-type cells, the mRNA are to in the mutant and in the The of these mutations are in the disruption induction is further to only of the mRNA observed in the wild-type These data are with the growth of the rtg mutant strains on medium containing oleic acid these findings indicate that the RTG genes, while required for CIT2 expression, are also important for oleic acid induction of other peroxisomal The from the strains used in the were by to whether oleic acid also induces expression of the glyoxylate cycle genes, CIT2, and As in the mRNA abundance of of these genes was increased in wild-type cells when grown in medium containing oleic acid. These data are with the of M.T. Veenhuis M. Trapp S.B. Goodman J.M. J. Bacteriol. 1990; 172: 5816-5827Google which from and cell of grown yeast cells, that the enzymes of the glyoxylate cycle are As we have both RTG1 and RTG2 are required for basal and expression of CIT2 in cells grown on X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). The of RTG1 for CIT2 expression is also in the induction of we could not any CIT2 mRNA in cells or the the that in wild-type cells, CIT2 mRNA abundance is increased when those cells are grown in the of oleic acid. The mRNA for and in the mutant was to of the wild-type Surprisingly, in cells grown in the of oleic acid, CIT2 mRNA was not only but its abundance was of the wild-type the RTG2 for basal CIT2 expression in cells grown on medium X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar) is when cells are grown on medium containing oleic acid. expression in cells was by only of for and the in an increase and in the abundance of the for these genes, suggesting that RTG2 can also as a The of oleic acid to increase expression of and is blocked in the that this growth condition RTG1 is to RTG2 for expression of these genes. The of the retrograde regulation of nuclear gene expression in to the functional state of mitochondria in S. One of the of the study was to the of the retrograde that whether other lesions in the tricarboxylic acid cycle the absence of CS1 activity also elicit an increase in CIT2 expression and whether other genes encoding glyoxylate cycle enzymes be subject to retrograde the we have that ρ+ cells containing a of the tricarboxylic acid cycle gene MDH1 also have an elevated of CIT2 mRNA to that observed in cells. This that CIT2 expression is not likely to be on mitochondrial CS1 CIT2 expression the functional of the tricarboxylic acid cycle is not In ρ+ cells with a of either or the increase in CIT2 mRNA abundance to wild-type ρ+ cells is not as as is observed in ρ0 petites. with that CIT2 expression also by growing wild-type ρ+ cells on a carbon in the of a chain X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google we that CIT2 retrograde control is likely to be a phenomenon the of mitochondrial other with a glyoxylate cycle, yeast is to acetate as a sole carbon on the glyoxylate cycle to two for Biochem. Scholar). from β-oxidation of fatty acids can be a of these which can from peroxisomes mitochondria through the H. M. J. A. 1993; Scholar). We suggested previously that the retrograde of CIT2 expression is a of the of and from the glyoxylate cycle to mitochondria, in to tricarboxylic acid cycle activity is X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google Scholar, A.W. Butow R.A. Current Biol. 1993; 3: 398-400Google Scholar). The findings that cells with mutant alleles of either RTG1 or RTG2 grow on acetate and are for which are characteristic of cells with blocks in both the tricarboxylic acid and glyoxylate M. Alam T. Kim K.-S. Clark B.J. Srere P.A. Guarente L.P. Mol. Cell. Biol. 1986; 6: 4509-4515Google is with the function of the RTG genes in communication between these A of mRNA abundance in ρ+ and in ρ0 cells of the three other glyoxylate cycle genes and shows that at this of the retrograde of glyoxylate cycle genes is for with that increased CIT2 expression compensates for a reduction in tricarboxylic acid cycle activity(5Liao X. Small W.C. Srere P.A. Butow R.A. Mol. Cell. Biol. 1991; 11: 38-46Google this that CS2 activity could be a in the glyoxylate We are in that it is not to a in the in of a metabolic P.A. Trends Biochem. Sci. 1994; 19: if the pathway has K. N. S. J. Biol. Chem. 1994; Scholar). Thus, while the is that CS2 activity is an important control point in the metabolic between the glyoxylate and tricarboxylic acid cycles, that will further Although and strains are unable to acetate as a sole carbon it possible that could by β-oxidation of long chain fatty acids in the growth We that the were also in their to oleic acid as a carbon source. The latter could be due to an of the mutant cells to by β-oxidation of oleic acid or to other in the pathway of oleic acid In an to this we examined the oleic acid induction of for three peroxisomal two of POX1 and CTA1 (encoding and are involved in the PMP27, encodes the most abundant protein associated with peroxisomal membranes in yeast and is required for oleic acid induction of wild-type peroxisomal P.A. Krimkevich Y.I. Lark R.H. Dyer J.M. Veenhuis M. Goodman J.M. J. Cell Biol. 1995; 129: 345-355Google Scholar, 21Erdman R. Blobel G. J. Cell Biol. 1995; 128: 509-523Google Scholar). expression is thus a for peroxisome The of these show that both RTG1 and RTG2 are required for full oleic acid induction of expression of these peroxisomal protein genes as in the oleic acid induction is by of the genes is in the single rtg mutant strains the for RTG2 is greater than these data point to a similarity of function between the RTG genes and genes that are required for peroxisome M. M. G. A. H. Yeast. 1992; 8: Scholar, M. B. 1993; Scholar, R. Veenhuis M. Kunau W.-H. Sci. U. S. A. Scholar, M. R. M. B. J. Cell Biol. 1992; Scholar). The oleic expression of a number of genes encoding peroxisomal proteins in yeast has to a sequence called an that is a site for transcription B. Eur. J. Biochem. 1993; Scholar, M. M.M. W. B. H. 1993; Scholar). Although the RTG2 not a protein or transcription the RTG1 has to be a basic helix-loop-helix transcription factor that binds to the upstream of CIT2 and is essential for its X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). One is that RTG1 is also a of the RTG1 not to to the upstream of the B. Eur. J. Biochem. 1993; which encodes the oleic peroxisomal enzyme and whose induction by oleic acid also requires We the that the RTG1 with other In any the similarity of of oleic acid induction of the gene in the and mutant strains that the RTG genes may be required at in the oleic acid induction of peroxisome A.S. Hines V. Small G.M. Mol. Cell. Biol. 1990; 10: 1399-1405Google Scholar) and M.T. Veenhuis M. Trapp S.B. Goodman J.M. J. Bacteriol. 1990; 172: 5816-5827Google Scholar) glyoxylate cycle enzymes in peroxisomes of yeast cells grown on medium containing oleic acid. The study to the of the of oleic acid on expression of genes encoding glyoxylate cycle enzymes in the oleic of expression are to the induction of expression of the genes studied the with the rtg are the large induction of CIT2 mRNA in wild-type ρ+ cells grown on medium containing oleic acid, CIT2 mRNA was in the or mutant were with cells grown on medium containing oleic acid not the of RTG1 for CIT2 X. Butow R.A. Cell. 1993; 72: 61-71Google Scholar). the genes, oleic acid induction of the glyoxylate cycle genes shows a greater for RTG1 than for In the absence of the RTG2 in an elevation in the mRNA abundance for and in cells grown on oleic acid These data show that the RTG2 can as both a and of peroxisomal gene expression. Finally, the of the it is that the RTG genes play a key role in a communication between mitochondria, the nucleus, and peroxisomes. We H. for to to We also J. Goodman and M. for of Finally, we for a of the and for