Range: ±0.1 bp
||Record MT Jr et al., Double helical DNA: conformations, physical properties, and interactions with ligands. Annu Rev Biochem. 1981 50 :997-1024. p.999 2nd paragraphPubMed ID7023371
|| Wang JC. Helical repeat of DNA in solution. Proc Natl Acad Sci U S A. 1979 Jan76(1):200-3.  Rhodes D, Klug A. Helical periodicity of DNA determined by enzyme digestion. Nature. 1980 Aug 7 286(5773):573-8.PubMed ID284332, 7402337
||Primary source  abstract: "The helical repeat of DNA in solution has been measured directly by analyzing the gel electrophoretic patterns of pairs of covalently closed DNAs with length differences between 1 and 58 base pairs, out of a total length of about 4350 base pairs per DNA molecule. The method is based on the observation that for a covalently closed DNA of a fixed size of n base pairs (n of the order of several thousand), under appropriate conditions, two topological isomers (topoisomers) differing by 1 in their linking numbers are well resolved by gel electrophoresis." Primary source  abstract: "The periodicity of DNA has been determined by binding short, stiff pieces of DNA to a flat surface and using DNase I to probe the accessibility of the phosphodiester bonds."
||P.999 2nd paragraph: "Using the band-shift method, which exploits the topological properties of closed circular DNA, Wang measured an average helical repeat of 10.6±0.1 (primary source 18 J. Wang, personal communication). The interpretation of the precise size distribution of DNA fragments produced by nuclease digestion of DNA immobilized on different surfaces gave a similar nonintegral value for the helical repeat of 10.6±0.1 (primary source 19). Related results from the nuclease digestion of nucleosome cores (refs 20, 21) can only yield model-dependent values (ref 22). Neither the bandshift nor the nuclease digestion techniques can distinguish between the reported smaller helical winding and a combination of right-handed helical winding and left-handed intrinsic writhe of the helix axis (ref 23)."