An additional class II intron with homology to reverse transcriptase in rapidly senescing Podospora anserina

Senescence in Podospora anserina is maternally inherited and the parameters of senescence are race specific. We have compared the restriction enzyme fragment maps of race A, the most rapidly senescing race, with race s and have found three inserts in race A which are not present in race s mitochondrial DNA. Fragment A was mapped and found to be located downstream of the so-called alpha senDNA, a class II intron, near the 5' end of the COI gene, separated from alpha senDNA by two class I introns. DNA sequence analysis showed that fragment A is also a class II intron, but with only 10% DNA sequence homology to alpha senDNA. Like alpha senDNA, intron A contains significant amino acid homology with known reverse transcriptases. The importance of this additional class II intron in the mitochondrial genome with the relative rate of senescence in race A is discussed.