Nucleic acid metabolism in yeast, V. Excretion of thymidylate

It is shown that highly efficient utilisers of exogenous dTMP of the yeast Saccharomyces cerevisiae are able to excrete the nucleotide with similar efficiency. Strains Pi-repressible in acid phosphatase/nucleotidase excrete dTMP at extracellular high Pi; strains constitutive for this enzymic activity excrete dThd. Excretion of thymidylate and dThd, unlike uptake of exogenous dTMP, seems to be unaffected by the extracellular pH, by the extracellular presence of dTMP, and to be rather independent of the extracellular presence of a metabolisable carbohydrate such as D(+)-glucose. A model of the yeast dTMP-incorporation principle (TIP) is presented suggesting that it is also responsible for export of endogenous thymidylate.