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. Author manuscript; available in PMC: 2009 Nov 1.
Published in final edited form as: Trends Cell Biol. 2008 Sep 27;18(11):521–527. doi: 10.1016/j.tcb.2008.08.005

Figure 1.

Figure 1

Assigning yeast Pol δ and Pol ε to specific strands. (a) During DNA synthesis in vitro, L612 M Pol δ generates T-dGMP errors at a rate that is at least 28-fold that of A-dCMP errors (green). (b) In a pol3-L612 M msh2- yeast strain, the T-A to C-G mutation rate (depicted earlier as the T to C substitution and depicted here as the inferred T-G mismatch [23]) is high (58 × 10-7) at base pair 97 in URA3 when present in orientation 1. Given the biased error rates in panel (a), these mutations are inferred to result from T-dGMP errors during lagging-strand synthesis by Pol δ. (c) In orientation 2, the mutation rate for the same base pair (base pair 97) in the same neighboring sequence context is much lower (3.10-7), implying that Pol δ has little role in leading-strand synthesis. Using this same logic, because Pol δ deletes template T in homopolymeric runs at a rate 11-fold that of what it deletes in template A [see (a)], L612 M Pol δ is inferred to delete a T-A base pair from a run of five T-A base pairs (174-178) during lagging-strand replication of template Ts [see (c)], but not during leading-strand replication of template As [see (b)]. Finally, note that M644G Pol ε generates T-dTMP errors at a rate ≥39-fold that of A-dAMP errors [blue in part (a)]. In a pol2-M644G strain, the T-A to A-T mutation rate is higher at base pair 686 in URA3 orientation 1. Given the biased error rates in panel (a), these mutations are inferred to result from T-dTMP errors during leading-strand replication by M644G Pol ε. In orientation 2 [see (c)], the mutation rate for the same base pair (base pair 686) in the same neighboring sequence context is much lower, implying that Pol ε has little role in lagging-strand synthesis. Additional examples of mutational specificity that are consistent with these interpretations can be found in Refs [12,23]. Part (a) adapted from Refs. [12,22]. Parts (b,c) adapted from Refs [12,23].