Abstract: RNase H,a ribonuclease specifically degrades the RNA chain in RNA:DNA hybrid,exists vastly in organisms from procaryotic to humanic.We use isothermal titration calorimetry to study the binding thermodynamics of Mg2＋,Mn2＋,Ca2＋ to a type II RNase H from an archaeon:Methanococcus jannaschii.For the first time we obtain the thermodynamic parameters of this binding reaction and verify that these metal ions bind with RNase HII with a ratio of 1:1.This will give an important information for studying RNase HII reaction mechanism and folding properties.

Key words: RNase HII, Isothermal titration calorimetry, Divalent metal ion