The mitochondrial DNA polymerase βfrom Crithidia fasciculata has 5′-deoxyribose phosphate (dRP) lyase activity but is deficient in the release of dRP

DNA polymerase β (pol β) has long been described as a nuclear enzyme involved in DNA repair. A pol β from the trypanosomatid parasite Crithidia fasciculata, however, is the first example of a mitochondrial enzyme of this type. The mammalian nuclear enzyme functions not only as a nucleotidyl transferase but also has a dRP lyase activity that cleaves 5′-deoxyribose phosphate (dRP) groups from DNA, thus contributing to two consecutive steps of the base excision repair pathway. We find that the mitochondrial pol β also has dRP lyase activity. Interestingly, the K_m of this enzyme for a dRP-containing substrate is similar to that for the rat enzyme, but its k_cat is very low. This difference is due to a deficiency of the mitochondrial enzyme in the release of dRP from the enzyme following its cleavage from the DNA.