Isolation and structural analysis of the phospho-beta-galactosidase gene from Streptococcus lactis Z268

A 4.4-kb XhoI fragment of Streptococcus lactis L13 (Z268) lactose plasmid pUCL13, containing the beta-D-phosphogalactoside galactohydrolase (P-beta Gal; EC 3.2.1.85)-coding gene has been cloned in Escherichia coli. Further subcloning and deletion of this fragment allowed localization of the P-beta Gal-coding gene (pbg) on a minimal 1.8-kb segment. Expression of P-beta Gal activity was constitutive and was not regulated by glucose in E. coli. The presence of P-beta Gal activity was correlated with the production of a 56.5-kDa protein in E. coli minicells. The nucleotide sequence of the cloned gene was determined and potential promoter structural elements were identified.