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The interactions of a purified calf thymus chromosomal non‐histone protein (designated protein HMG1) with bacteriophage T7 DNA and calf thymus DNA have been investigated by sedimentation analysis in the ultracentrifuge. The results obtained show that (a) the non‐histone protein HMG1 binds to DNA in an ionic‐strength‐dependent manner, (b) the DNA can bind up to approximately four to five times its weight of protein HMG1, the protein distributing itself evenly along the DNA chains, and (c) the interaction is a rapid reversible equilibrium. These results are interpreted as indicating that protein HMG1 binds to DNA through ionic bonding between the basic amino acids of the protein and the phosphate groups of the DNA. 2. Equilibrium sedimentation studies were carried out on mixtures of protein HMG1 and histone F1. The results demonstrate that protein HMG1 combines with histone F1. 3. The molecular weight of protein HMG1 has been determined by equilibrium sedimentation and a mean value of 26500 was obtained.
Shooter et al. (1974) studied this question.