MASC2, A C5-DNA-METHYLTRANSFERASE FROM ASCOBOLUS-IMMERSUS WITH SIMILARITY TO METHYLTRANSFERASES OF HIGHER ORGANISMS

The filamentous fungus Ascobolus immersus represents an eukaryotic mod el organism to study genetic phenomena linked to DNA methylation. Foll owing our previous characterization of a gene, masc1 from A. immersus, encoding the 'de novo' C5-DNA-methyltransferase (MTase), we report he re the identification of a second MTase gene, masc2. The deduced pepti de sequence of Masc2 is similar to previously identified eukaryotic MT ases and distinct from Masc1 by having a large N-terminal domain in ad dition to the ubiquitous C-terminal catalytic domain. Following clonin g of the gene, Masc2 was overexpressed and purified. Masc2 shows MTase activity with double stranded DNAs. Structural and biochemical proper ties of Masc2 suggest that it may function as a 'maintenance' MTase. W ith this finding, A. immersus represents so far the only eukaryotic or ganism in which two possibly synergistically operating MTases have bee n identified.