Sequence specificity of the P1 modification methylase (M· Eco P1) and the DNA methylase (M· Eco dam) controlled by the Escherichia coli dam gene

Labeled oligonucleotides have been fractionated from pancreatic DNase digests of DNA that had been methylated in vitro with the P1 modification enzyme (M· Eco P1) or with the DNA-adenine methylase (M· Eco dam) controlled by the Escherichia coli dam gene. The sequences of methylated oligonucleotides were established for M· Eco dam modification of calf thymus DNA. The results show that M· Eco dam inethylates adenine residues contained in the twofold symmetrical sequence, 5′ … G-A-T-C … 3′. The sequence for the site methylated by M· Eco P1 has also been deduced; we propose that M· Eco P1 modification produces the following methylated pentameric sequence: 5′ … A-G-A ∗-C-Py … 3′ (where A ∗ = N 6 methyladenine and Py is C or T).