Members of the RTP (receptor transporter proteins) family have recently been discovered to influence bitter taste receptor expression in addition to inducing the expression of mammalian odorant receptors. RTP3 is a 232 amino acid single-pass type III membrane protein belonging to the TMEM7 family. Unlike other RTP proteins, RTP3 is not expressed in olfactory neurons but is expressed predominantly in liver. RTP3 is involved in the functional expression of bitter taste receptors and suppresses cell proliferation, and is also found in human circumvallate papillae and testis (regions where bitter taste receptors are expressed). The gene encoding RTP3 maps to human chromosome 3p21.31 within C3CER1 (chromosome 3 common eliminated region 1), which is frequently eliminated in chromosomal deletions of solid tumors.