Galactose and lactose metabolism in S. thermophilus , reproduced from Johansen et al . (A). Abbreviations: LacS, lactose transporter; LacZ, β-galactosidase; GlcK, glucose kinase; GalM, mutarotase; GalK, galactokinase; PGM, α-phosphoglucomutase; GalT, galactose 1-phosphate udridyltransferase; GalE, UDP glucose 4-epimerase; GalU, UDP glucose pyrophosphorylase; gal1P, galactose-1-phosphate; g1p, glucose-1-phosphate; g6p, glucose-6-phosphate; UDP-glu, UDP-glucose; and UDP-gal, UDP-galactose. (B) The promoter region of the galactose operon; the mutation in the Pribnow box of the mutant strain in bold and marked (*). The enhanced expression of galK is indicated by a thickened arrow in the pathway and an arrow in the promoter region of the operon.