DNA products obtained from a linear 615 bp pUC19 DNA fragment treated with T4 DNA ligase in the form of naked DNA at increasing DNA concentrations. The 1.3% agarose gel in 0.5× TAE buffer contained 1 µg/ml ethidium bromide and was run at 80 V. Lanes 1–4 show the ligation products resulting from the ligation of DNA at 0.4, 4, 8 and 16 µg/ml, respectively. These concentrations are approximately equivalent to those used in Figure 2 on a molar basis. DCC, NC, L and CC denote the dimer closed circle, nicked circle, linear and monomer closed circle form of the DNA fragment, respectively. The lane labeled U contained unligated DNA; lane M contained a 123 bp linear DNA ladder. The bracket on the right indicates high MW DNA ligation products.