A new Thermus sp class-IIS enzyme sub-family:: isolation of a 'twin' endonuclease TspDTI with a novel specificity 5′-ATGAA(N11/9)-3′, related to TspGWI, TaqII and Tth111II -: art. no. e74

The TspDTI restriction endonuclease, which shows a novel recognition specificity 5'-ATGAA(N-11/9)-3', was isolated from Thermus sp. DT. TspDTI appears to be a 'twin' of restriction endonuclease TspGWI from Thermus sp. GW, as we have previously reported. TspGWI was isolated from the same location as TspDTI, it recognizes a related sequence 5'-ACGGA(N-11/9)-3' and has conserved cleavage positions. Both enzymes resemble two other class-IIS endonucleases from Thermus sp.: TaqII and Tth111II. N-terminal amino acid sequences of TspGWI tryptic peptides exhibit 88.9-100% similarity to the TaqII sequence. All four enzymes were purified to homogeneity; their polypeptide sizes (114.5-122 kDa) make them the largest class-IIS restriction endonucleases known to date. The existence of a Thermus sp. sub-family of class-IIS restriction endonucleases of a common origin is herein proposed.