Open AccessMolecular and genetic characterization of lactose-metabolic genes of Streptococcus cremoris
Author(s) -
Julia M. Inamine,
L N Lee,
Donald J. LeBlanc
Publication year - 1986
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.167.3.855-862.1986
Subject(s) - biology , microbiology and biotechnology , southern blot , plasmid , escherichia coli , dna , restriction enzyme , gene , complementation , transformation (genetics) , structural gene , lac operon , genetics , mutant
Lac+ plasmid DNA from Streptococcus cremoris H2 was subcloned with an Escherichia coli vector on a 3.5-kilobase-pair PstI-AvaI fragment. Genetic analysis of the cloned DNA was possible because linear Lac+ DNA fragments were productive in the S. sanguis transformation system. Complementation of S. sanguis Lac-mutants showed that the 3.5-kilobase-pair fragment included the structural gene for 6-phospho-beta-D-galactosidase and either enzyme II-lac or factor III-lac of the lactose-specific phosphoenolpyruvate-dependent phosphotransferase system. Expression of the S. cremoris-like 40,000-dalton 6-phospho-beta-D-galactosidase in S. sanguis Lac+ transformants, rather than the 52,000-dalton wild-type S. sanguis enzyme, demonstrated the occurrence of gene replacement and not gene repair. The evidence supports chromosomal integration as the mechanism by which S. sanguis Lac- recipients are converted to a Lac+ phenotype after transformation with Lac+ DNA. Southern blot data suggest that the Lac+ DNA does not reside on a transposon, but that integration always occurs within a specific HincII fragment of the recipient chromosome. Hybridization experiments demonstrate homology between the S. cremoris Lac+ DNA and cellular DNA from Lac+ strains of Streptococcus lactis, S. mutans, S. faecalis, and S. sanguis.