| Abstract: | A cDNA encoding the precursor of the bovine mitochondrial phosphate carrier protein has been cloned from a bovine cDNA library using a mixture of 128 different 17-mer oligonucleotides as hybridisation probe. The protein has an N-terminal extension of 49 amino acids not present in the mature protein. This extension has a net positive charge and is presumed to direct the import of the protein from the cytoplasm to the mitochondrion. Comparison of the protein sequence of the mature phosphate carrier with itself, with ADP/ATP translocase and with the uncoupling protein from brown fat mitochondria shows that all three proteins contain a 3-fold repeated sequence approximately 100 amino acids in length, and that the repeats in the three proteins are related to each other. This implies that the three proteins have related three-dimensional structures and mechanisms and that they share a common evolutionary origin. The distribution of hydrophobic residues in the phosphate carrier protein suggests that each repeated 100 amino acid element is composed of two membrane-spanning alpha-helices linked by an extensive hydrophilic domain. This model is similar to that first proposed for the ADP/ATP translocase and later for the brown fat mitochondria uncoupling protein. |
