The lacE and lacG genes from Streptococcus mutans have been isolated and characterized, and their nucleotide sequence has been determined. The lacE gene encodes the lactose-specific Enzyme II component of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The lacG gene encodes the phospho-β-galactosidase which cleaves the lactose phosphate that is formed by the lactose PTS. The S. mutans lacE and lacG genes are located in the same operon as the tagatose genes. S. mutans metabolizes lactose via the tagatose phosphate pathway. The deduced LacE and LacG proteins of S. mutans display high homology with the mg proteins from Lactococcus lactis, Staphylococcus aureus and Lactobacillus casei.
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