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J Biol Chem. 1999 Sep 3;274(36):25682-90.

Stable association of 70-kDa heat shock protein induces latent multisite specificity of a unisite-specific endonuclease in yeast mitochondria.

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  • 1Laboratory of Cellular and Molecular Biology, RIKEN (the Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan.


The multisite-specific endonuclease Endo.SceI of yeast mitochondria is unique among endonucleases because its 50-kDa subunit forms a stable dimer with the mitochondrial 70-kDa heat shock protein (mtHSP70), which otherwise fulfills a chaperone function by binding transiently to unfolded proteins. Here we show that the mtHSP70 subunit confers broader sequence specificity, greater stability, and higher activity on the 50-kDa subunit. The 50-kDa subunit alone displayed weaker activity and highly sequence-specific endonuclease activity. The 50-kDa protein exists as a heterodimer with mtHSP70 in vivo, allowing Endo.SceI to cleave specifically at multiple sites on mitochondrial DNA. Endo.SceI may have evolved from a highly specific endonuclease that gained broader sequence specificity after becoming a stable partner of mtHSP70.

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