Abstract
The ataxia-telangiectasia mutated (ATM) and AT-rad3+ related (ATR) protein family is highly conserved in all eukaryotes. It is well characterized as cell-cycle checkpoint kinases and their disruptions cause instability of nuclear genome. In S. cerevisiae, ATR protein Mec1 regulates an inhibitor of ribonucleotide reductase (RNR) that is involved in dNTP synthesis. Since decreases in dNTP levels preferentially affect mitochondrial DNA (mtDNA) replication in comparison to chromosomal DNA (chrDNA) replication, Mec1 indirectly controls mtDNA copy number. In metazoans, however, the effect of ATR on dNTP pools or mtDNA copy number has not been examined. Therefore, we have examined the involvement of C. elegans ATR checkpoint protein ATL-1 in maintenance of mtDNA.
In C. elegans, both mtDNA and chrDNA copy numbers increased in association with germline proliferation. atl-1 mutants exhibited a roughly equal rate of chrDNA accumulation but a reduced rate of mtDNA accumulation. On the other hand, no reductions were detected in mutants defective for atm-1 and cep-1, which are checkpoint related genes. RNR expression and the ATP/dATP ratio remained unaltered in atl-1 mutants, and inhibition of RNR caused further reductions in mtDNA copy number. These results indicate ATL-1 likely affects mtDNA levels by a novel mechanism independently of RNR and dNTP pools.
