Identification and characterization of PaMTH1, a putative O-methyltransferase accumulating during senescence of Podospora anserina cultures

A differential protein display screen resulted in the identification of a 2 7-kDa protein which strongly accumulates during the senescence of Podospora anserina cultures grown under standard conditions. After partial determina tion of the amino-acid sequence by mass-spectrometry analysis of trypsin-ge nerated fragments, pairs of degenerated primers were deduced and used to am plify parts of the sequence coding for the protein. These PCR products were utilized to select specific cDNA and genomic clones from DNA libraries of P. anserina. A subsequent DNA-sequence analysis revealed that the 27-kDa pr otein is encoded by a discontinuous gene, PaMth1, capable of coding for 240 amino acids. The first three amino-terminal residues appear to be removed post-translationally. The deduced amino-acid sequence shows significant hom ology to S-adenosylmethionine (SAM)-dependent methyltransferases. We hypoth esize that the 27-kDa protein, PaMTH1, is involved in age-related methylati on reactions protecting aging cultures against increasing oxidative stress.