A COMPARISON OF DNA METHYLATION LEVELS IN SELECTED ISOLATES OF HIGHERFUNGI

The extent of cytosine methylation in the DNAs of four basidiomycetes and two ascomycetes has been determined by RP-HPLC. The highest levels of 5-methyldeoxycytidine ((5m)dC) were found in the homobasidiomycete s Agaricus bisporus and Armillaria bulbosa (with 4.01 +/- 0.93% and 4. 34% +/- 1.03% of the cytosine residues methylated, respectively). The two heterobasidiomycetes examined also contained (5m)dC, but at lower levels; (2.26 +/- 0.31% for Ustilago maydis and 2.14 +/- 0.21% for U. violaceae). The DNA of the dimorphic ascomycete Ophiostoma novo-ulmi s howed a (5m)dC content ranging from 1.37 +/- 0.11% to 1.67 +/- 0.39%, depending on the isolate and the morphological stage. Methylated bases were not detected in Saccharomyces cerevisiae. No general correlation between strain degeneration and enhanced or decreased methylation cou ld be found in the commercial mushroom A. bisporus. The possible impli cation of extensive DNA methylation in genetic transformation of homob asidiomycetes using the bacterial gene for hygromycin phosphotransfera se as a selectable marker is discussed.