Nicotinamide Riboside Allows NAD+ Synthetase-Independent Growth Via a Novel Pathway
(A) qns1 cells transformed with a plasmid carrying the QNS1 and URA3 genes were tested for growth on synthetic dextrose complete media and 5-fluoroorotic acid (5-FOA). NAD+ synthetase mutant qns1 is inviable without supplements or with 1 mM nicotinamide but is rescued by 10 μM nicotinamide riboside.
(B) Strains with indicated mutations were plated on medium supplemented with 5-FOA and 10 μM nicotinamide riboside. Deletion of genes for uridine/cytosine kinase, adenosine kinase, and ribokinase do not alter the ability of yeast cells to utilize nicotinamide riboside.