Existence of two translation initiation sites leading to the expression of two proteins from the rat high-affinity neurotensin-receptor cDNA: Possible regulation by the 5' end non-coding region

This work demonstrates the expression of two different proteins (47 and 44 kDa) from the rat high-affinity neurotensin receptor cDNA, observed after both translation in vitro and transient transfection into eukaryotic COS-7 cells, These two proteins are the consequence of two initiation sites of translation present in the corresponding mRNA. Site-directed mutagenesis indicated that the 47 kDa protein was generated from the first AUG codon (Met(1)). In contrast, suppression of the second AUG codon found in the sequence (Met(27)) did not modify the expression of the two proteins previously observed with the wild-type neurotensin receptor. Therefore this second translation site could correspond to a non-AUG codon, Moreover, when the 5' end untranslated region of the neurotensin receptor mRNA is deleted, the expression of the higher-molecular-mass protein is enhanced, indicating that this region could be involved in the regulation of expression of these two proteins.