Abstract
Human sweet taste perception is mediated by the heterodimeric G protein-coupled receptor encoded by the TAS1R2 and TAS1R3 genes. Variation in these genes has been characterized, but the functional consequences of such variation for sweet perception are unknown. We found that two C/T single-nucleotide polymorphisms (SNPs) located at positions -1572 (rs307355) and -1266 (rs35744813) upstream of the TAS1R3 coding sequence strongly correlate with human taste sensitivity to sucrose and explain 16% of population variability in perception. By using a luciferase reporter assay, we demonstrated that the T allele of each SNP results in reduced promoter activity in comparison to the C alleles, consistent with the phenotype observed in humans carrying T alleles. We also found that the distal region of the TAS1R3 promoter harbors a composite cis-acting element that has a strong silencing effect on promoter activity. We conclude that the rs307355 and rs35744813 SNPs affect gene transcription by altering the function of this regulatory element. A worldwide population survey reveals that the T alleles of rs307355 and rs35744813 occur at lowest frequencies in European populations. We propose that inherited differences in TAS1R3 transcription account for a substantial fraction of worldwide differences in human sweet taste perception.