Sequence and Chromosomal Assignment of a Novel cDNA Identified by Immunoscreening of a Thyroid Expression Library: Similarity to a Family of Mitochondrial Solute Carrier Proteins

Abstract

An immunoglobulin G (IgG) preparation of the serum from a patient with active Graves'' disease was used to isolate cDNA clones from a .lambda.gt11 cDNA library of human thyroid follicular carcinoma tissue by immunoscreening. One of thes clones, hML-7, is further characterized herein by sequencing, Northern analysis, and chromosomal mapping. The clone reacted with IgG preparations from the sera of 14 of 19 patients with active Graves'' disease but not with IgG preparations from 11 normal individuals, three patients with toxic thyroid adenoma, and three with rheumatoid arthritis. The hML-7 cDNA hybridized to a 3.6 kilobase (kb) mRNA transcript in poly(A+)RNA preparations from human thyroid tissue and continuously cultured rat thyroid cells; expression of this transcript in rat FRTL-5 thyroid cells was positively regulated by TSH. The 3.6 kb transcript was less abundant in rat liver (BRL3A) cells or differentiated rat (L6) myoblasts than in cultured rat thyroid cells and was not detectable in mouse L-M fibroblasts, human IM-9 lymphocytes, Chinese hamster ovary cells, or human cervical carcinoma cells. The cDNA from hML-7 was sequenced and compared with the sequence of cross-hybridizing cDNA clones isolated from human Graves'' thyroid and rat FRTL-5 thyroid cell .lambda.gt11 expression libraries. A 1.05 kb open reading frame, which is highly conserved between human and rat, was defined. The predicted amino acid sequence of 348 residues exhibited a strong homology with the mitochonrial ADP/ATP carrier protein (adenine nucleotide translocase; ADP/ATP translocator) and with two other members of the same mitochondrial protein family, the phosphate carrier and the hydrogen ion uncoupling protein. The gene represented by the hML-7 cDNA has been assigned to human chromosome 10.