Characterization of a histone-like protein extracted from yeast mitochondria.

Analysis of proteins isolated by affinity chromatography on DNA-cellulose from highly purified yeast mitochondria shows that these organelles do not contain histones but have in abundance a DNA-binding protein of 20,000 daltons. The purification yield of this protein, called HM, indicates that mitochondria have at least an equal mass of HM relative to DNA. The amino acid composition and its electrophoretic characterization reveal that HM, rich in lysine, is slightly basic and heat stable. HM appears to be coded by the yeast nucleus, as shown by its presence in several "petite" mutants. We have shown that HM, like histones or histone-like proteins, is able to introduce superhelical turns into circular relaxed DNA in the presence of a nicking-closing activity.