A DNA polymerase beta in the mitochondrion of the trypanosomatid Crithidia fasciculata.
We previously purified a Crithidia fasciculata mitochondrial DNA polymerase that has unusual properties. Unlike a conventional mitochondrial DNA polymerase gamma, this enzyme is small, non-processive, deficient in 3'-exonuclease activity, and error prone (Torri, A. F., Kunkel, T. A., and Englund, P. T. (1994) J. Biol. Chem. 269, 8165-8171). In all of these characteristics, the enzyme resembles DNA polymerase beta, a nuclear enzyme thought to be involved in DNA repair. We have now cloned and sequenced the gene for this enzyme. The mitochondrial polymerase has significant homology, about 33% identity at the amino acid level, with human DNA polymerase beta. However, sequence analysis of the clone revealed the presence of a cleaved N-terminal presequence, presumably a mitochondrial import signal, which resembles presequences on other C. fasciculata mitochondrial proteins. The polymerase's function may be to repair the many gaps in newly replicated kinetoplast (mitochondrial) DNA minicircles in this parasite. This enzyme is the first example of a mitochondrial DNA polymerase beta.
Torri
A F
AF
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Englund
P T
PT
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016831:Crithidia fasciculata / Q000201:enzymology*; D004256:DNA Polymerase I / Q000235:genetics*; D016054:DNA, Protozoan; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
D016054:DNA, Protozoan; D004256:DNA Polymerase I