[Cloning and expression of the gene for thermostable beta-galactosidase from Thermoanaerobacter ethanolicus in Escherichia coli: purification and properties of the product].

An anaerobic thermophilic bacterium Thermoanaerobacter ethanolicus 39E (Clostridium thermohydrosulfuricum 39E) gene library was constructed in E. coli. Recombinant plasmid (pUT50) containing the thermostable beta-galactosidase was isolated by direct selection of clones for enzyme activity using 5-bromo-4-chloro-3-indolyl-D-galactopyranoside (X-gal) and mapping procedures were carried out. The beta-galactosidase was purified from cell extracts of E. coli. Physicochemical characteristics of the recombinant beta-galactosidase were determined. The enzyme has two optimum pH values: 5.3 and 6.0, the temperature optimum is 75-80 degrees C. The molecular weight of beta-galactosidase was determined by PAG electrophoresis: about 83 kDa.