Abstract
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.
Highlights
We previously purified a Crithidia fasciculata mitochondrial DNA polymerase that has unusual properties
In all of these characteristics, the enzyme resembles DNA polymerase 13, a nuclear enzyme thought to be involved in DNA repair
A protozoan parasite related to the trypanosomes, has an unusual mitochondrial DNA known as kinetoplast DNA.1 kDNA consists of 5000 minicircles and 25 maxicircles, all of which are topologically interlocked into one giant network
Summary
We previously purified a Crithidia fasciculata mitochondrial DNA polymerase that has unusual properties. The mitochondrial polymerase has significant homology, about 33% identity at the amino acid level, with human DNA polymerase p. The polymerase's function may be to repair the many gaps in newly replicated kinetoplast (mitochondrial) DNA minicircles in this parasite.
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