At the chromatin level, methylated CpG dinucleotides are R.Msp1 resistant compared with nonmethylated counterparts. The DNA of two E.coli strains was analyzed following transformation-with bacterial cytosine-5-methyltransferase gene M.Msp1 in mammalian transfection vector pcDNA3. Expression of the M.Msp1 was tested by R.Msp1 digestion. The results suggest that the DNA of both strains was fully methylated at the CCGG sequences, by the active enzyme under the control of T7 and cytomegalovirus (CMV) promoters. Methylated DNA can not be digested and it exhibits higher frag-ment sizes in 1% agarose gel in contrast to the untransformed cell DNAs in vivo.

At the chromatin level, methylated CpG dinucleotides are R.Msp1 resistant compared with nonmethylated counterparts. The DNA of two E.coli strains was analyzed following transformation-with bacterial cytosine-5-methyltransferase gene M.Msp1 in mammalian transfection vector pcDNA3. Expression of the M.Msp1 was tested by R.Msp1 digestion. The results suggest that the DNA of both strains was fully methylated at the CCGG sequences, by the active enzyme under the control of T7 and cytomegalovirus (CMV) promoters. Methylated DNA can not be digested and it exhibits higher frag-ment sizes in 1% agarose gel in contrast to the untransformed cell DNAs in vivo.