HYPERMETHYLATION AT CPG-MOTIFS IN THE DINOFLAGELLATES AMPHIDINIUM-CARTERAE (DINOPHYCEAE) AND SYMBIODINIUM-MICROADRIATICUM (DINOPHYCEAE) - EVIDENCE FROM RESTRICTION ANALYSES, 5-AZACYTIDINE AND ETHIONINE TREATMENT

Because of their peculiar chromatin features and phylogenetic position , dinoflagellates are potentially uniquely informative with respect to possible roles and evolution of DNA methylation systems. Here we repo rt that DNA from Amphidinium carterae Hulburt and Symbiodinium microad riaticum Freudenthal was not significantly digested by a range of CpG methylation-sensitive endonucleases. Corresponding methylation-insensi tive isoschizomers cleaved all DNA preparations. Treatment with the me thylation inhibitors 5-azacytidine and ethionine resulted in major inc reases indigestibility of dinoflagellate DNA by CpG methylation-sensit ive enzymes. The 5-azacytidine effect was not confined to heterochroma tin. Our studies indicate that at least in some dinoflagellates, a hig h proportion of CpG motifs and a significant number of CpNpG motifs ar e normally methylated, implying methyltransferase substrate specificit ies similar to those of higher plants.