title: Absence of cytosine methylation at C-C-G-G and G-C-G-C sites in the rDNA coding regions and intervening sequences of Drosophila and the rDNA of other insects.
abstract: Cytosine residues in C-G dinucleotides are frequently methylated in eukaryote DNA. In DNA of the dinoflagellate C. cohnii, the sequence C-MeC-G-G apparently renders Hpa II (C-C-G-G) incapable of digesting whole cell DNA in general, and rDNA in particular. Msp I, which also recognizes C-C-G-G but cleaves irrespective of methylation, degrades C. cohnii DNA and produces rDNA segments of 10.2 to 1.4 kb. We have applied this Hpa II/Msp I test to unfractionated DNA, and to rDNA and the rDNA intervening sequence of Drosophila virilis embryos and adults. There is no evidence of C-MeC-G-G sequences in either developmental stage of this species. Absence of G-MeC-G-C from coding and intervening sequences of rDNA was shown in comparisons of Hha I (G-C-G-C) cleavage patterns of unfractionated DNA and cloned (unmodified) segments of rDNA. Comparisons of Hpa II and Msp I cleavage products of DNA from the house fly, the flesh fly and a bumblebee also revealed no internal cytosine methylation in the sequence C-C-G-G. Because amounts of McC in C-G dinucleotides vary greatly among species, from apparent nonexistence to substantial proportions, no inference may yet be drawn about the role of such base modifications in DNA.
mesh_terms: D000818:Animals; D001483:Base Sequence; D001516:Bees / Q000032:analysis; D003596:Cytosine / Q000032:analysis; D004247:DNA / Q000378:metabolism; D004262:DNA Restriction Enzymes; D004175:Diptera / Q000032:analysis; D004330:Drosophila / Q000032:analysis*; D006793:Houseflies / Q000032:analysis; D007313:Insecta / Q000032:analysis*; D008745:Methylation; D013045:Species Specificity
chemical_list: D003596:Cytosine; D004247:DNA; D004262:DNA Restriction Enzymes