Polymerase Switching in DNA Replication Susan T. Lovett  Molecular Cell  Volume 27, Issue 4, Pages 523-526 (August 2007) DOI: 10.1016/j.molcel.2007.08.003 Copyright © 2007 Elsevier Inc. Terms and Conditions

Figure 1 The Trombone Model for Coupled Leading- and Lagging-Strand Polymerization, as Modeled for the E. coli Replisome Two DNA polymerases (turquoise) bound to processivity clamps (blue rings) are coupled to each other and to the fork helicase (tan hexagon) via interactions with τ (orange) of the clamp loader complex (other subunits in green). RNA primers (purple) to initiate Okazaki fragments are synthesized by primase (yellow) associated with the helicase. Molecular Cell 2007 27, 523-526DOI: (10.1016/j.molcel.2007.08.003) Copyright © 2007 Elsevier Inc. Terms and Conditions

Figure 2 Polymerase Exchange, as in the T7 Bacteriophage Replication System Only leading-strand synthesis is shown for simplicity. DNA polymerase (turquoise oval) is bound to the primer terminus and template and tightly associated with the fork helicase (tan hexagon). Other polymerases (blue oval) can bind more loosely to other sites on the helicase. The engaged polymerase releases the terminus transiently, allowing polymerase exchange. Molecular Cell 2007 27, 523-526DOI: (10.1016/j.molcel.2007.08.003) Copyright © 2007 Elsevier Inc. Terms and Conditions

Figure 3 The Three-Polymerase Replisome of E. coli (A) Three DNA polymerases (turquoise) are coupled to each other and to the fork helicase (tan hexagon) via interactions with τ (orange) of the clamp loader complex (other subunits in green). RNA primers synthesized by primase (yellow) to initiate Okazaki fragments are shown in purple. Two polymerases are engaged in synthesis, bound to processivity clamps (blue rings); one is in reserve. (B) Transient dissociation of one of the polymerases, leaving a β clamp and 3′ end free to engage repair factors. (C) Reassociation of DNA polymerase with the clamp, with polymerase exchange. (D) Engagement of all three polymerases, one on the leading strand and two on the lagging strand. Molecular Cell 2007 27, 523-526DOI: (10.1016/j.molcel.2007.08.003) Copyright © 2007 Elsevier Inc. Terms and Conditions