Transcriptional regulation of the Saccharomyces cerevisiae DAL5 gene family and identification of the high affinity nicotinic acid permease TNA1 (YGR260w).

We have studied the transcript levels of YGR260w and YLR004c, two genes encoding members of the yeast Dal5p subfamily of the major facilitator family, and we show that they increase when extracellular nicotinic acid and thiamine, respectively, are absent. The deletion of YGR260w in a bna1 auxotrophic mutant for nicotinic acid prevents growth at low nicotinic acid concentration. This suggests that YGR260w is necessary for nicotinic acid import into the cell. The direct measurement of nicotinic acid uptake on whole cells demonstrates that YGR260w encodes the yeast high affinity nicotinic acid permease. Its apparent K(m) of 1.7 microM is low enough to allow the uptake of the low concentrations of nicotinic acid normally secreted by wild type cells.