Cleavage at the twelve-base-pair sequence 5′-TCTAGATCTAGA-3′ using M·Xbal(TCTAGm6A) methylation andDpnl(Gm6A/TC) cleavage

Abstract

The DNA methylase M·Xbal was isolated from an E. coli recombinant clone. We deduce that the enzyme methylates at the sequence 5′-TCTAG^m6A-3′. In combination with the methyiation-dependent restriction endonuclease, Dpnl (5′-G^m6A/TC-3′), DNA cleavage occurs at the sequence 5′-TCTAGA/TCTAGA-3′. This twelve-base-pair site should occur once every 16,000,000 base pairs in a random sequence of DNA. The exceptional rarity of the M·Xbal/Dpnl sequence makes it an ideal candidate for transpositional integration of a unique cleavage site into bacterial genomes. Retrotransposition into mammalian genomes is also an attractive possibility.