Alternative translation initiation codon for the human melanocortin MC₃ receptor does not affect the ligand binding

The genomic DNA for the human melanocortin MC₃ receptor indicates an unusually long N-terminus. Two possible translation initiation sites, the one originally proposed and one alternate 111 bp downstream, were mutated. For a third mutant the DNA between these initiation sites was deleted. All mutants were expressed in COS (CV-1 Origin, SV40) cells in the same level, and they bound peptide hormones in the same fashion, as did the wild type clone. The data obtained indicate that both sites can function as the sole translation initiation sites of the human clone and-that the proposed N-terminus of the human melanocortin MC, receptor is not important for the ligand binding of the receptor.