Sequential events and corresponding "gates" controlling pol β's fidelity: the conformational change avenue, which comprises of Asp192 flip, Phe272 flip, and Arg258 rotation accompanying the thumb subdomain closing motions upon substrate binding, the pre-chemistry avenue, which involves the stochastic reorganization of the protein catalytic region, particularly the coordinating ligands of the two binding metal ions, and the chemistry avenue, where the incoming nucleotide is finally connected onto the primer terminus so that the primer is extended by one residue.
Reference:
Radhakrishnan, R.; Arora, K.; Wang, Y.; Beard, W. A.; Wilson, S. H.; Schlick, T. Biochemistry; (Current Topics/Perspectives); 2006; 45(51); 15142-15156.