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Mol Cell. 2001 Jan;7(1):43-54.

Crystal structure and deletion analysis show that the accessory subunit of mammalian DNA polymerase gamma, Pol gamma B, functions as a homodimer.

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Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.


Polymerase gamma, which replicates and repairs mitochondrial DNA, requires the Pol gamma B subunit for processivity. We determined the crystal structure of mouse Pol gamma B, a core component of the mitochondrial replication machinery. Pol gamma B shows high similarity to glycyl-tRNA synthetase and dimerizes through an unusual intermolecular four-helix bundle. A human Pol gamma B mutant lacking the four-helix bundle failed to dimerize in solution or to stimulate the catalytic subunit Pol gamma A, but retained the ability to bind with Pol gamma A to a primer-template construct, indicating that the functional holoenzyme contains two Pol gamma B molecules. Other mutants retained stimulatory activity but lost the ability to bind folded ssDNA. These results suggest that the Pol gamma B dimer contains distinct sites for Pol gamma A binding, dimerization, and DNA binding.

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