Relationship between the Purity and Molecular Weight of Calf Thymus DNA

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Abstract
The MW and purity of calf thymus DNA, prepared by different procedures of isolation, were determined. The highest MW was obtained by the method of Blin and Stafford (12 .times. 107). This DNA contained 17% protein. The further purification of this DNA led both to increase of purity and to reduction of the MW. The relationship between MW and achieved purity was found to be a monotonic sigmoid-shape function ranging between the MW of 12 .times. 107 and 12 .times. 106 and between the purities of 17 and 0.7% protein. After achieving this highest level of purity (0.7% protein content), despite repetition of the purification cycles, no further increase of purity or reduction of the MW was achieved. The use of [14C]T4 bacteriophage DNA as internal standard demonstrated that the reduction of the MW does not result from an artifact, such as shear or enzymatic degradation, but that the high-MW calf thymus DNA preparation must be considered to consist of either aggregates of small subunits stabilized by laterally attached proteins or of tandemly joined units connected by protein or peptide linkers.

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