Mitochondrial telomere-binding protein from Candida parapsilosis suggests an evolutionary adaptation of a nonspecific single-stranded DNA- binding protein

Abstract

The mitochondrial genome in a number of organisms is represented by linear DNA molecules with defined terminal structures. The telomeres of linear mitochondrial DNA (mtDNA) of yeast Candida parapsilosis consist of tandem arrays of large repetitive units possessing single-stranded 5' extension of about 110 nucleotides. Recently we identified the first mitochondrial telomere-binding protein (mtTBP) that specifically binds a sequence derived from the extreme end of C. parapsilosis linear mtDNA and protects it from attack by various DNA-modifying enzymes (Tomaska, L'., Nosek, J., and Fukuhara, H. (1997) J. Biol. Chem. 272, 3049-3059). Here we report the isolation of MTP1, the gene encoding mtTBP of C. parapsilosis. Sequence analysis revealed that mtTBP shares homology with several bacterial and mitochondrial single-stranded DNA-binding proteins that nonspecifically bind to single-stranded DNA with high affinity. Recombinant mtTBP displays a preference for the telomeric 5' overhang of C. parapsilosis mtDNA. The heterologous expression of a mtTBP-GFP fusion protein resulted in its localization to the mitochondria but was unable to functionally substitute for the loss of the S. cerevisiae homologue Rimlp. Analysis of the MTP1 gene and its translation product mtTBP may provide an insight into the evolutionary origin of linear mitochondrial genomes and the role it plays in their replication and maintenance.