Mutations affecting levels of tetrahydrofolate interconversion enzymes in Saccharomyces cerevisiae

Lam, Keng-Bon; Jones, Elizabeth W.

doi:10.1007/bf00271238

Cited by 9 publications

(1 citation statement)

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“…5,lO-Methylenetetrahydrofolate dehydrogenase was assayed by a modification of the methods utilized Lam et al [13] and Scrimgeour et al [14]. The assay system was 216 mM phosphate buffer pH 7.5, 34 mM potassium ascorbate pH 6.0, 0.58 mM formaldehyde, 0.2 mM tetrahydrofolate, 0.6 mM NADP (or 3 mM NADP for the mitochondrial enzyme) in a total volume of 1.2ml.…”

Section: Enzyme Assaysmentioning

confidence: 99%

Mitochondrial and Cytoplasmic Distribution in Saccharomyces cerevisiae of Enzymes Involved in Folate‐Coenzyme‐Mediated One‐Carbon‐Group Transfer

Zelikson

Luzzati

1977

European Journal of Biochemistry

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The study of the subcellular distribution of the enzymes involved in folate-coenzyme-mediated transfer of one-carbon groups in Saccharomyces cerevisiae suggests the existence of two parallel enzyme systems, one mitochondrial and the other cytoplasmic. All the enzymes assayed in the present study, serine transhydroxymethylase, dihydrofolate reductase, 5,lO-methylenetetrahydrofolate dehydrogenase, 10-formyltetrahydrofolate synthetase, 5,lO-methylenetetrahydrofolate reductase and thymidylate synthetase were found to be in both cytoplasm and mitochondria. Two of the mitochondrial enzymes, serine transhydroxymethylase and dihydrofolate reductase, were found to be different by several criteria from their cytoplasmic counterparts.By the use of three nuclear gene mutations ade3, tmp3 and serl, and different combinations of these three mutations, the physiological role of the cytoplasmic enzymes for the biosynthesis of adenine, histidine, methionine, thymidylate and serine was studied. The response of auxotrophes to an external source of tetrahydrofolate, i. e. 5-formyl tetrahydrofolic acid, was also examined. The mitochondrial set of enzymes might be responsible for the de novo formation of tetrahydrofolate, since the loss of the three mitochondrial enzyme activities, serine transhydroxymethylase, thymidylate synthetase and dihydrofolate reductase, due to the mutation tmp3, leads to a generalized requirement for thymidylate, methionine, adenine and histidine. The ade3 mutation in which the cytoplasmic activities of the 10-formyltetrahydrofolate synthetase, 5,lO-methenyltetrahydrofolate cyclohydrolase and 5,lO-methylenetetrahydrofolate dehydrogenase are lost, confers only adenine and histidine auxotrophy, showing that the ade3 proteins are synthesized in, and only function in, the cytoplasm. The mitochondrial counterparts of these enzymes may function solely in the formation of the 10-formyl tetrahydrofolate needed for the transformylation of Met-tRNA involved in mitochondrial protein synthesis.A study of a nuclear mutation in Saccharomyces cerevisiae, tmp3, leading concomittantly to multiple nutritional requirements for thymidylate, methionine, adenine and histidine and to the petite phenotype, was found to have a decreased activity of serine transhydroxymethylase, but a wild-type level of two other tetrahydrofolate-linked enzymes, 10-formylte- trahydrofolate-linked enzymes, 10-formyltetrahydrofolate synthetase and 5,1O-methylenetetrahydrofolate dehydrogenase [l]. Further study showed that wildtype strains of yeast have two forms of serine transhydroxymethylase, one cytoplasmic and the other mitochondrial, separable by TEAE-cellulose chromatography. The mutant tmp3 has lost the mitochondrial form [2].Serine transhydroxymethylase may be the major physiological source of 5,lO-methylene tetrahydrofolate needed for the formation of methionine, thymidylate and adenine. Loss of the mitochondrial enzyme, in tmp3, which leads to that multiple requirement, implies that either the mitochondrial serine transhydroxymethylase is the...

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Section: Enzyme Assaysmentioning

confidence: 99%

Mitochondrial and Cytoplasmic Distribution in Saccharomyces cerevisiae of Enzymes Involved in Folate‐Coenzyme‐Mediated One‐Carbon‐Group Transfer

Zelikson

Luzzati

1977

European Journal of Biochemistry

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The phenoloxidases of the ascomycete Podospora anserina

Prillinger

Esser

1977

Molec. Gen. Genet.

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1. Eight mutants were isolated following mutagen treatment which are deficient in laccase formation. Seven of these had a pleiotropic effect and exhibited defects in growth rate and in mycelial and sexual morphology. 2. By means of tetrad analysis the mutations were assigned to 6 loci. Three mutations were in the incolora locus, the others were non-allelic. Only two of these loci were closely linked. 3. All genes exhibit numerous interactions. These concern the morphological expression of the laccase genes and also the laccase spectra. 4. The mutants could be separated into four classes on the basis of the amount and type of laccase produced. 5. Five of the loci studied appear to be structural genes because mutations alters the physical properties of the laccase protein. The sixth gene has a regulatory role.

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