CLEAVAGE AT THE 12-BASE-PAIR SEQUENCE 5'-TCTAGATCTAGA-3' USING M.XBAL (TCTAGM6A) METHYLATION AND DPNI (GM6A/TC) CLEAVAGE

The DNA methylase M·Xbal was isolated from an E. coli recombinant clone. We deduce that the enzyme methylates at the sequence 5′-TCTAGm6A-3′. In combination with the methyiation-dependent restriction endonuclease, Dpnl (5′-Gm6A/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. © 1990 Oxford University Press.