Escherichia coli exonuclease III enhances long PCR amplification of mtDNA from heat-damaged mouse liver DNA templates. Qiagen-extracted mouse liver DNA was heated at 99°C for 30–120 s and two distinct regions of the mtDNA were co-amplified with Protocol 1a using 14 pmol of primers for the 316 bp PCR product and 40 pmol for the 8636 bp PCR product. Lanes 1–4 correspond to aliquots of the same mouse liver DNA sample heated for 30, 60, 90 and 120 s, respectively. Agarose gels (1.2%) were loaded with 22 µl of the products. M is Hin dIII-digested phage λ DNA (fragment sizes 23.1, 9.4, 6.6, 4.4, 2.3, 2.0 and 0.56 kb). ( A ) PCR reactions were performed without exonuclease III (exo 0) or with 25 U of exonuclease III (exo 25 U). ( B ) PCR reactions were performed with either 5 or 1 U of exonuclease III (exo 5 U and exo 1 U) or with 25 U of exonuclease III preheated at 99°C for 10 min (preheated exo).