Isoschizomers of the restriction endonuclease TaqI (T/CGA) requiring different metal ion concentrations and having a range of thermal stabilities from Thermus species from different continents.

One-hundred-and-fifty-two isolates of the genus Thermus, collected from hot springs on four continents, were screened for evidence of the presence of the thermophilic Type II restriction endonuclease TaqI (T/CGA). The presence of isoschizomers of TaqI in 27 of the isolates, originating from hot springs in New Zealand, Iceland, USA, Japan, mainland Portugal and the island of São Miguel in the Azores, is reported. Six of the TaqI-containing isolates from diverse geographical locations, identified by means of DNA/DNA homology and 16S rRNA sequence alignment as belonging to the Thermus species T. aquaticus, T. filiformis, T. thermophilus, T. scotoductus and T. brockianus, were selected for comparative studies. The TaqI isoschizomers from each of the six isolates were partially purified. They differed in their magnesium ion requirements, isoelectric points, subunit molecular masses and thermal stability.