ACCESSORY SUBUNIT OF MITOCHONDRIAL-DNA POLYMERASE FROM DROSOPHILA EMBRYOS - CLONING, MOLECULAR ANALYSIS, AND ASSOCIATION IN THE NATIVE ENZYME

A full-length cDNA of the accessory (beta) subunit of mitochondrial DN A polymerase from Drosophila embryos has been obtained, and its nucleo tide sequence was determined. The cDNA clone encodes a polypeptide wit h a deduced amino acid sequence of 361 residues and a predicted molecu lar mass of 41 kDa. The gene encoding the beta subunit lies within 4 k ilobase pairs of that for the catalytic subunit in the Drosophila geno me, on the left arm of chromosome 2. The two genes have similar struct ural features and share several common DNA sequence elements in their upstream regions, suggesting the possibility of coordinate regulation. A human cDNA homolog of the accessory subunit was identified, and its nucleotide sequence was determined. The human sequence encodes a poly peptide with a predicted molecular mass of 43 kDa that shows a high de gree of amino acid sequence similarity to the Drosophila beta subunit. Subunit-specific rabbit antisera, directed against the recombinant ca talytic and accessory subunit polypeptides overexpressed and purified from Escherichia coli, recognize specifically and immunoprecipitate th e native enzyme from Drosophila embryos. Demonstration of the physical association of the two subunits in the Drosophila enzyme and identifi cation of a human accessory subunit homolog provide evidence for a com mon heterodimeric structure for animal mitochondrial DNA polymerases.