Cloning, DNA sequence, and regulation of expression of a gene encoding (β-galactosiclase from Lactococcus lactis

Abstract

The β-galactosidase frorh Escherichia coli is one of the most important enzymes in molecular biology. Here we report the cloning and sequencing of a gene encoding β-galactosidase from Lactococcus lactis and compare the predicted amino acid sequence to that from other organisms. The (β-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% similarity to the enzyme from Klebsiella pneumoniae. The lactococcal β-galactosidase has lower similarity (approx 55%) to the enzymes from other lactic acid bacteria and no significant similarity to the β-galactosidase enzymes from Agrobacterium radiobacter, Bacillus stearothermophilus, or Clostridium thermosulfurogenes. Expression of the lacZ gene from I. lactis was found to be higher when cells were grown in medium containing lactose than when grown in glucose, and expression was higher when cells were grown at 30°C than at 35°C.

Key Words:

• Lactic Acid Bacteria
• β-galactosidase, LacZ
• Cloning Vectors
• Expression
• Regulation