Four DNA sequences (ARSs) that are able to initiate DNA replication
in yeast were isolated from mitochondrial DNA of
Phytophthora nicotianae and localized on its physical map. Nuclear
sequences from P. nicotianae were shown to initiate DNA
replication in yeast only very rarely. Minimal regions necessary for
replication catalysed by mitochondrial ARSs were delimited by
DNase I digestion and sequenced. Transformation efficiencies were estimated
for full-length ARS-carrying DNA fragments.
Segregation rates and mitotic stabilities in S. cerevisiae were
determined for the two shortest subclones of each of the three delimited
ARSs. Replication properties of all three ARSs were similar to those of
a yeast nuclear ARS sequence. Sequence analysis revealed the
presence of many copies of the motif (T/G)ATATTTT, which is related
to the ARS core consensus sequences, in all three elements.
In two of them, four copies of the motif and its reverse complements
were arranged in palindromes. In addition, whole ARS core
sequences and long segments consisting exclusively of A and T nucleotides
were found in all ARS analysed. These features indicate
that an HMG-like (high mobility group) DNA-binding protein similar to ABF2
from yeast may participate in DNA packaging also in
non-fungal mitochondrial lineages.