C. Jametvierny et al., INTRAMOLECULAR CROSS-OVERS GENERATE DELETED MITOCHONDRIAL-DNA MOLECULES IN PODOSPORA-ANSERINA, Current genetics, 31(2), 1997, pp. 162-170
The unavoidable senescence process that limits the vegetative growth o
f Podospora anserina is always associated with an accumulation of vari
ous classes of circular, tandemly arranged, defective mitochondrial DN
A molecules (senDNAs). The monomers of the senDNAs belonging to the so
-called beta class share a common core, but differ in both their lengt
h and termini. To understand the mechanism leading to their formation,
we have determined the junction sequence of 36 senDNA beta monomers p
resent in various senescent cultures. In most cases, we observe that:
(1) short direct repeats precisely bound the senDNA beta termini and (
2) one copy of the repeats is retained in the senDNA sequence. Moreove
r, PCR analysis of the mitochondrial DNA of some of the senescent cult
ures, has allowed us to detect another genome which is exactly lacking
the sequence of the senDNA beta found in the culture. These results d
emonstrate that an intramolecular unequal cross-over occurring between
short direct repeats can generate deleted mtDNA molecules in P. anser
ina. In addition, the polymorphism displayed by one pair of repeats al
lows us to establish that this cross-over may be associated with a sho
rt conversion tract spanning a few (about 15) nucleotides.