Howard M. Goodman

Location and nucleotide sequence of the site on SV40 DNA methylated by the ECO B modification methylase

Summary The modification methylase from Escherichia coli strain B, Eco B, introduces two methyl groups into one SV40 DNA molecule. The only base methylated has been identified as N6-methyladenine. Digestion of the methylated SV40 DNA with two restriction endonucleases, one from Hemophilus influenzae , Hind III, and another from Hemophilus aegyptius , Hae , locates the methyl groups in the same DNA fragment, about 250 base pairs long, between 0.860 and 0.907 fractional lengths of SV40 DNA clockwise from the Eco RI site on the circular SV40 genome. Analysis of dinucleoside monophosphates, trinucleoside diphosphates, and tetranucleoside triphosphates, generated by partial digestion of the methylated DNA with pancreatic DNase I gave the following sequences of nucleotides at the site(s) of methylation by the Eco B methylase: 5′…C-m6A-G-C-T…3′ and 5′…T-G-m6A-A…3′ These cannot be incorporated into a simple sequence with 2-fold rotational symmetry.