Laayoun A, Baker D J, Riley J, Smith S S
Department of Cell and Tumor Biology, City of Hope Medical Center, Duarte, CA 91010.
Gene. 1994 Dec 2;150(1):195-6. doi: 10.1016/0378-1119(94)90884-2.
Synthetic oligodeoxyribonucleotide duplexes have been used to study the methylation specificity of M.HpaII, a bacterial DNA methyltransferase. Substrates of four types were compared. A 30-mer containing a Watson-Crick paired CCGG recognition sequence was rapidly methylated at the central cytosine on each strand in the recognition sequence. A 30-mer containing an asymmetrically methylated recognition sequence, of the type transiently produced by DNA replication, was rapidly methylated at the central cytosine on the unmethylated strand. A heteroduplex containing an A.C mispair in the recognition sequence (CCGG/CCAG) was rapidly methylated at the cytosine in the mispair. A heteroduplex containing an A.C and an adjacent C.C mispair in the recognition sequence (CCGG/CCCA) was not methylated at a significant rate. The results show that M.HpaII can tolerate a single mispair at its recognition site in a heteroduplex without loss of activity or specificity.
