The Accessory Subunit of Xenopus laevis Mitochondrial DNA Polymerase γ Increases Processivity of the Catalytic Subunit of Human DNA Polymerase γ and Is Related to Class II Aminoacyl-tRNA Synthetases

• DOI: 10.1128/mcb.19.6.4039
• Publication Date: 2015-10-26T10:18:57Z
• Authors: José A. Carrodeguas; Ryuji Kobayashi; Susan E. Lim; William C. Copeland; Daniel F. Bogenhagen
• Keywords: 0301 basic medicine; 0303 health sciences; Dose-Response Relationship, Drug; Sequence Homology, Amino Acid; Molecular Sequence Data; Magnesium Chloride; DNA-Directed DNA Polymerase; DNA, Mitochondrial; Precipitin Tests; DNA Polymerase gamma; Potassium Chloride; Amino Acyl-tRNA Synthetases; Xenopus laevis; 03 medical and health sciences; Animals; Humans; Electrophoresis, Polyacrylamide Gel; Amino Acid Sequence; Cloning, Molecular

Peptide sequences obtained from the accessory subunit of Xenopus laevis mitochondrial DNA (mtDNA) polymerase gamma (pol gamma) were used to clone the cDNA encoding this protein. Amino-terminal sequencing of the mitochondrial protein indicated the presence of a 44-amino-acid mitochondrial targeting sequence, leaving a predicted mature protein with 419 amino acids and a molecular mass of 47.3 kDa. This protein is associated with the larger, catalytic subunit in preparations of active mtDNA polymerase. The small subunit exhibits homology to its human, mouse, and Drosophila counterparts. Interestingly, significant homology to glycyl-tRNA synthetases from prokaryotic organisms reveals a likely evolutionary relationship. Since attempts to produce an enzymatically active recombinant catalytic subunit of Xenopus DNA pol gamma have not been successful, we tested the effects of adding the small subunit of the Xenopus enzyme to the catalytic subunit of human DNA pol gamma purified from baculovirus-infected insect cells. These experiments provide the first functional evidence that the small subunit of DNA pol gamma stimulates processive DNA synthesis by the human catalytic subunit under physiological salt conditions.