Cloning and characterization of cDNA for mitochondrial GTP:AMP phosphotransferase of bovine liver.

Three different types of cDNA clones for mitochondrial GTP:AMP phosphotransferase (AK3) were isolated from a cDNA library of bovine liver poly(A)+ RNA. Nucleotide sequencing revealed that each of these clones consisted of a common 5'-untranslated region, a common AK3-coding sequence and a 3'-untranslated region with different sizes. By Northern blot analysis, three species of AK3 mRNA apparently corresponding to the isolated cDNA clones were detected, which would be a result of varying terminations and polyadenylations of the primary transcript. From comparison of the size of the product synthesized in vitro from the message directed by the isolated cDNA with that of the purified AK3 protein, AK3 appeared to have no cleavable NH2-terminal sequence as found in other mitochondrial proteins. The AK3 cDNA was expressed in Escherichia coli, which resulted in complementation of an adenylate kinase mutation of E. coli. The AK3 product was exported to the periplasmic space through the bacterial inner membrane. The possible involvement of the NH2-terminal sequence of the protein in targeting to the mitochondrial matrix was discussed.