Yeast strains carrying recessive mutations representing four different loci that cause defects in pyruvate kinase, pyruvate decarboxylase, 3-phosphoglycerate kinase, and 3-phosphoglycerate mutase were isolated and partially characterized. Cells carrying these mutations were unable to use glucose as a carbon source as measured in turbidimetric growth experiments. Tetrad analysis indicated that these mutations were not linked to each other; one of the mutations, that affecting phosphoglycerate kinase, was located on chromosome III.

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Standard laboratory yeast strains can be enriched for thymidine 5'-monophosphate (TMP) uptake derivatives that generate only a low percentage of respiratory-deficient colonies (petites) under inhibition of TMP biosynthesis. Such mutants incorporated bromodeoxyuridine 5'-monophosphate (BrdUMP) into both nuclear and mitochondrial deoxyribonucleic acid (mtDNA); however, they showed a selectivity for TMP over BrdUMP incorporation. The preferential incorporation of [3H]TMP or BrdUMP into mtDNA was strain dependent. The density increments after growth in the presence of BrdUMP reached 50 mg/ml for nuclear DNA and 22 mg/ml for mtDNA in CsCl gradients. Density shifts correspondisng to 4% bromouracil substitution were easily detected. Preliminary density transfer experiments confirm that mtDNA does not replicate in synchrony with nuclear DNA.

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