Unwinding of DNA by nonhistone protein HMG1 and HMG2.
The enzyme kinetic studies with endonucleases specific for single-stranded DNA and the thermal denaturation analyses of DNA showed that a high mobility group (HMG) nonhistone protein fraction HMG (1 + 2), composed of HMG1 and HMG2, has an activity to unwind DNA partially at low protein-to-DNA weight ratio. Isolated HMG1 and HMG2 have the same activity. Divalent cations such as Mg++ or Ca++ were necessary for the unwinding reaction. A peptide containing high glutamic and aspartic (HGA) region, isolated from the tryptic digest of HMG (1 + 2), unwound DNA depending on the presence of Mg++ or Ca++, suggesting that the HMA region in HMG protein is the active site for the DNA unwinding reaction. Poly-L-glutamic acid, employed as a model peptide of the HGA region, showed the activity. Finally, mechanisms of the DNA unwinding reaction by the HMG protein and possible role of the divalent cations are discussed.
D000818:Animals; D004265:DNA Helicases / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D006609:High Mobility Group Proteins / Q000378:metabolism*; D007700:Kinetics; D009492:Neurospora crassa / Q000201:enzymology; D009691:Nucleic Acid Denaturation; D013552:Swine; D013816:Thermodynamics; D013950:Thymus Gland
D004277:DNA, Single-Stranded; D006609:High Mobility Group Proteins; D003850:Deoxyribonuclease I; D004265:DNA Helicases