Cloning and Genetic Validation of Yeast and Human Nicotinamide Riboside Kinases
(A) HPLC traces of a negative pool (36) and positive pool (37) of GST-ORF fusions. In pool 36, some ATP was converted to ADP and production of AMP occurred in several pools including 37. In pool 37, approximately half of the 1 mM ATP was converted to ADP and the 500 μM Nr peak was almost entirely converted to NMN.
(B) Amino acid sequence alignment of human Nrk1, human Nrk2, S. cerevisiae Nrk1, S. pombe nrk1, and portions of S. cerevisiae uridine/cytidine kinase Urk1 and E. coli pantothenate kinase.
(C) nrk1 deletion introduced into a qns1 deletion strain blocks the ability to form colonies in the presence of nicotinamide riboside. Expression of human NRK1 or human NRK2 cDNAs restores growth to qns1 nrk1 deletion strains, indicating that human Nrk1 and Nrk2 are authentic nicotinamide riboside kinases in vivo.