CLONING, DNA-SEQUENCE, AND REGULATION OF EXPRESSION OF A GENE ENCODING BETA-GALACTOSIDASE FROM LACTOCOCCUS-LACTIS

The beta-galactosidase from Escherichia coli is one of the most import ant enzymes in molecular biology. Here we report the cloning and seque ncing of a gene encoding beta-galadosidase from Lactococcus lactis and compare the predicted amino acid sequence to that from other organism s. The beta-galactosidase from L. lactis was found to be a protein of 996 residues with 68.7% similarity to the E. coli enzyme and 65.8% sim ilarity to the enzyme from Klebsiella pneumoniae. The lactococcal beta -galactosidase has lower similarity (approx 55%) to the enzymes from o ther lactic acid bacteria and no significant similarity to the beta-ga lactosidase enzymes from Agrobacterium radiobacter, Bacillus stearothe rmophilus, or Clostridium thermosulfurogenes. Expression of the lacZ g ene from L. lactis was found to be higher when cells were grown in med ium containing lactose than when grown in glucose, and expression was higher when cells were grown at 30 degrees C than at 35 degrees C.