An Endonuclease from Yeast Mitochondrial Fractions

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Abstract
A membrane-bound endonuclease was isolated from mitochondrial fractions of S. cerevisiae. The enzyme is present in a stable complex and has an approximate MW of 14000. It requires Mg2+ or Mn2+ for activity, and has an optimum pH of 7.0. Its activity with native DNA is 5 times less than with denatured DNA in 0.05 M KCl and is very low in 0.2 M KCl. The activity with RNA is 40% of that with denatured DNA; the 2 substrates are competitive. Its mode of action is endonucleolitic, it cuts both strands of native .lambda. DNA at the same or nearby sites. After mild digestion of DNA, analysis of 5''-end groups of the digestion products indicated a marked preference for deoxythymidylic and deoxyguanilic acid residues as the site of enzymatic cleavage. After exhaustive digestion of DNA, mononucleotides (2.4%), dinucleotides (70.5%) and trinucleotides (27%) ending in 5''-phosphate are produced.