The genomic DNAs of the eukaryotic Chlorella-like green alga, strain NC64A, and eleven of its viruses all contain significant levels of 5-methyldeoxycytidine. In addition, the host DNA as well as six of the viral DNAs also contain N6-methyldeoxyadenosine. At least some of the methylated bases in the host reside in different base sequences than the nethylated bases in the viruses as shown by differential susceptibility to restriction endonuclease enzymes. This suggests that the viruses encode for DNA methyltransferases with sequence specificities different from that of the host enzyme.
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