dim-2 encodes a DNA methyltransferase responsible for all known cytosine methylation in Neurospora

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Abstract
To understand better the control of DNA methylation, we cloned and characterized the dim‐2 gene of Neurospora crassa , the only eukaryotic gene currently known in which mutations appear to eliminate DNA methylation. The dim‐2 gene is responsible for methylation in both symmetrical and asymmetrical sites. We mapped dim‐2 between wc‐1 and un‐10 on linkage group (LG) VIIR and identified the gene by RFLP mapping and genetic complementation. Dim‐2 encodes a 1454 amino acid protein including a C‐terminal domain homologous to known DNA methyltransferases (MTases) and a novel N‐terminal domain. Neither a deletion that removed the first 186 amino acids of the protein nor a mutation in a putative nucleotide binding site abolished function, but a single amino acid substitution in the predicted catalytic site did. Tests for repeat‐induced point mutation (RIP) indicated that dim‐2 does not play a role in this process, i.e. duplicated sequences are mutated in dim‐2 strains, as usual, but the mutated sequences are not methylated, unlike the situation in dim‐2+ strains. We conclude that dim‐2 encodes an MTase that is responsible for all DNA methylation in vegetative tissues of Neurospora .