Growth of tna1, tnr1, and tnr2 mutant strains is compromised at low concentrations of NAD+ vitamin precursors. (A) Growth of six strains on medium with 0.5 μM NA, NAM, or NR as the sole source of NAD+. The relevant genotypes of the strains are wild type (WT; strain BG2), tna1 (BG1441), tnr1 (BG1338), tnr2 (BG1335), tnr1 tnr2 (BG1337), and tna1 tnr1 tnr2 (BG1447). The cells are able to grow equally well if supplemented with excess NAD+ precursors (8 μM NA, 4 μM NAM, and 32 μM NR; at concentrations of one-half of these levels, growth of the relevant transporter mutants is compromised relative to that of the wild type). (B) Complementation of the growth defect of tna1 tnr1 tnr2 mutants. Strain1442 was transformed with an empty expression vector or with vectors expressing TNA1, TNR1, or TNR2, and growth was assessed on SC plates containing 0.5 μM NA, NAM, or NR. (C) The tna1 tnr1 tnr2 mutant C. glabrata strain was transformed with plasmids expressing S. cerevisiae ORFs YGR260w (TNA1), YOR192c (THI72), YOR071c (NRT1), and YLR237w (THI7). These strains were plated on SC-URA-NA plates supplemented with 0.5 μM NA, NAM, or NR.