Protein bound to mitochondrial DNA from tumor and normal tissues of humans and animals

Stable mitochondrial (mt) DNA-protein complexes have been reported repeatedly in the last decade. We have found that the amount of proteins bound to mt DNA was increased in human HL-60 promyelocytic and chronic myelocytic leukemia cells. Mt of human tumor cells and bovine and rate liver cells were isolated by differential centrifugation. The DNA was purified by SDS-NaCl precipitation of protein, alcohol precipitation, and sucrose density gradient centrifugation. Mt DNA-bound protein obtained by enzymatic digestion of the DNA and purified by gel exclusion and reverse-phase HPLC chomatographies and SDS-polyacrylamide gel electrophoresis, showed a major protein band at 70 kD and a minor band at 35 kD. Hydrolysis of the mtDNA-protein complex in formic acid yielded DNA bases and peptides by HPLC on a C18 reverse-phase column. Tumor cell mtDNA contained 5-10 times more bound protein than mtDNA from normal tissue.