Regulation of sucrose-6-phosphate hydrolase activity in Streptococcus mutans: characterization of the scrR gene.
Previous results have implicated an important role for the enzyme IIScr, the sucrose-specific permease, in the transport of sucrose by cariogenic Streptococcus mutans. The product of the scrB gene, sucrose-6-phosphate hydrolase (Suc-6PH), is required for the metabolism of phosphorylated sucrose. The results from the utilization of scrB::lacZ fusions in S. mutans GS-5 have suggested that sucrose-grown cells have higher levels of scrB gene expression than do cells grown with glucose or fructose. Northern blot analysis of scrB transcripts has also confirmed the relative strengths of expression as sucrose>glucose>fructose. Immediately downstream from the scrB gene, an open reading frame with homology to regulatory proteins of the GalR-LacI family as well as to ScrR proteins from several other bacteria has been identified. In addition, this gene appears to be transcribed in the same operon as scrB. Inactivation of this gene, scrR, did not alter the relative expression of the scrB gene in the presence of sucrose or fructose but did increase SUC-6PH levels in the presence of glucose to that observed with sucrose. Furthermore, the S. mutans ScrR homolog appears to bind to the scrB promoter region as determined from the results of gel shift assays. These results suggest that the scrR gene is involved in the regulation of scrB, and likely scrA, expression. However, it is not clear whether sucrose acts as an inducer of expression of these genes or, alternatively, whether glucose and fructose act as repressors.
Department of Oral Biology, State University of New York, Buffalo, New York 14214, USA.
K
K
Hiratsuka
B
B
Wang
Y
Y
Sato
H
H
Kuramitsu
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D015964:Gene Expression Regulation, Bacterial; D006026:Glycoside Hydrolases / Q000235:genetics* / Q000378:metabolism; D007763:Lac Operon; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics; D014158:Transcription, Genetic; D043324:beta-Fructofuranosidase
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C083535:scrR protein, bacteria; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase