Disease relevance of scrB

• Sequence analysis of the Streptococcus mutans scrB gene [1].
• Sequence analysis of scrA and scrB from Streptococcus sobrinus 6715 [2].
• The Streptococcus mutans GS-5 gene, scrB, coding for sucrose 6-phosphate hydrolase activity has been cloned into Escherichia coli utilizing the bacteriophage replacement vector lambda L47 [3].
• The deduced amino acid sequence of the gene product of S. sobrinus scrB shared strong homology with sucrase from Bacillus subtilis, Klebsiella pneumoniae, and Vibrio alginolyticus, suggesting conservation based on the physiological roles of these proteins [2].
• Toward this end, we have now constructed and evaluated three Escherichia coli-S. mutans shuttle expression vectors with the fruA and scrB promoters from S. mutans, as well as the tetR-controlled tetO promoter from Staphylococcus aureus [4].

High impact information on scrB

• These results suggest that the scrR gene is involved in the regulation of scrB, and likely scrA, expression [5].
• 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 [5].
• Furthermore, the S. mutans ScrR homolog appears to bind to the scrB promoter region as determined from the results of gel shift assays [5].
• 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 [5].
• In addition, this gene appears to be transcribed in the same operon as scrB [5].

Chemical compound and disease context of scrB

• The complete nucleotide sequences of Streptococcus sobrinus 6715 scrA and scrB, which encode sucrose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system and sucrose-6-phosphate hydrolase, respectively, have been determined [2].
• Mutants of Streptococcus mutans V403 defective in the intracellular sucrose-6-phosphate hydrolase (product of the scrB gene) are sensitive to sucrose because of the intracellular accumulation of the phosphorylated sugar [6].
• Sucrose catabolism by Streptococcus mutans is initiated by a phosphoenolpyruvate-dependent sucrose phosphotransferase reaction that produces sucrose 6-phosphate the latter is then cleaved by a sucrose 6-phosphate hydrolase reaction that yields glucose 6-phosphate and fructose [7].

Biological context of scrB

• These data indicate that the three genes are clustered on the GS-5 chromosome, with ftf located between gtfA and scrB [8].
• One, O(C), which includes a 20-bp imperfect inverted-repeat sequence, is located between the two promoters, and the other, O(B), is located within the scrB promoter region containing a 37-bp imperfect direct-repeat sequence [9].
• The Streptococcus mutans GS-5 scrA gene coding for enzyme IIScr of the phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS) was localized upstream from the scrB gene coding for sucrose-6-phosphate hydrolase activity after Mu dE transposon mutagenesis of plasmid pMH613 [10].

Associations of scrB with chemical compounds

• Using a scrB mutant prepared by allelic exchange, we have isolated and characterized a number of sucrose-resistant revertants [6].
• 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 [5].

Other interactions of scrB

• However, gtfA cotransferred with ftf and scrB at frequencies of approximately 96 and 80%, respectively [8].
• Thus, a Tetr gene was inserted adjacent to gtfB in the appropriate mapping vector and within the ftf and scrB genes with a mini-Mu transposon (Mu dT) [8].

Analytical, diagnostic and therapeutic context of scrB

• Northern blot analysis of scrB transcripts has also confirmed the relative strengths of expression as sucrose>glucose>fructose [5].

References