Looking for promiscuous DNA in hemiascomycetous genomes.
Odile Ozier-Kalogeropoulos (1), Christine Sacerdot (1), Serge Casaregola (2), Fredj Tekaia (1), Norio Gunge (3), Kohsai Fukuda (3), Bernard Dujon (1)
(1) Struct. et Dyn. des Genomes, Institut Pasteur, 25 rue du Dr Roux, Paris, 75724, France; (2) Laboratoire de Microbiologie et Genetique Moleculaire, INRA UMR1238, CNRS/INA-PG UMR 2585, 78850 Thiverval-Grignon, France; (3) Sojo-University, Ikeda 4-22-1, Kumamoto, 860-0082, Japan
Transfer of organelle DNA to the nuclear genome is a general phenomenon in Eukaryotes. In the yeast Saccharomyces cerevisiae, fragments homologous to mitochondrial DNA were previously found and it was shown that colonization of the nuclear genome by mitochondrial DNA is an ongoing process (Ricchetti et al, 1999, Nature, 402, 96-100; Yu and Gabriel (1999), Mol Cell, 4, 873-881). Here, we analyse the NUMT content of the nuclear genome of the four other hemiascomycetous yeasts sequenced by the Genolevures consortium ( Candida glabrata, Kluyveromyces lactis, Debaryomyces hansenii and Yarrowia lipolytica ). We observe interspecies variations of NUMTs number, which do not correlate with the length of the mitochondrial DNA. NUMTs in the genome of C. glabrata are slightly less abundant (two-fold) than those of S. cerevisiae and of comparable small size (20-300bp). D. hansenii is the one showing the most abundant fragments (ten-fold more than in S. cerevisiae ). In some cases, chimeric fragments are also observed. Two of these yeasts, K. lactis and D. hansenii harbor cytoplasmic linear plasmids. Sequences homologous to these plasmids were also found in their nuclear genomes with D. hansenii containing the higher number of such sequences. The way these DNA fragments invaded the nuclear genome is presently unknown. The accurate examination of the composition of these promiscuous DNA fragments should give indications on the mechanism of the transfer.