A site specific endonuclease from Thermus thermophilus 111, Tth1111

A site specific endonuclease with novel specificity has been isolated from Thermus thermophilus strain 111 and named Tth111I. Tth111I cleaves λ DNA into three fragments of 23.5, 25.7 and 50.8 % of the total length, and ColE1 DNA into two fragments of nearly equal length. The sequences around Tth111I cleavage sites of ColE1 and λ DNA were determined by the Maxam and Gilbert method and the two dimensional mapping method. The results suggest that Tth111I recognizes the DNA sequence $↓5'-TGACNNNGTC-3′3′-ACTGNNNCAG-5′↑$ and cleaves the site as indicated by the arrows. Assuming that the first T. A pair in the sequence can be replaced for any base pair, the Tth111I recognition sequence has the symmetry with the two-fold axis as most type II restriction endonucleases do.