Jackson Laboratory, Bar Harbor, Maine 04609.
The mitochondrial uncoupling protein, a protein essential for the thermogenic properties of brown fat in mammals, is inserted in the inner mitochondrial membrane by means of six alpha-helical hydrophobic transmembrane domains. We have sequenced a complete cDNA and parts of the gene to determine that the mitochondrial uncoupling protein gene is composed of six exons, each of which encodes a transmembrane domain. We also show that transcription of the uncoupling protein gene is from a single start site; however, the use of alternative poly(A) addition signal sequences results in two mRNAs, the major species of 1221 nucleotides, not including the poly(A) tail, and a minor species of about 1600 nucleotides. The 5'-untranslated region of the mRNA is composed of 231 nucleotides, and the 3'-untranslated region contains 81 nucleotides prior to addition of the poly(A) tail.