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A 10.2-kb gene region was identified in the  Streptococcus pneumoniae  genome sequence that contains eight genes involved in regulation and metabolism of raffinose. The genes  rafR  and rafS  are transcribed as one operon, and their gene products regulate the raffinose-dependent stimulation of a divergently transcribed second promoter ( P A  ) directing the expression of  aga , the structural gene for α-galactosidase. Raffinose-mediated transcription from  P A   results in a 500-fold increase in α-galactosidase activity in the cell. A third promoter within the cluster is responsible for the transcription of the remaining five genes ( rafE, rafF, rafG , gtfA , and  rafX ), whose gene products might be involved in transport and metabolism of raffinose. The presence of additional internal promoters cannot be excluded. The  aga promoter  P A   is negatively regulated by the presence of sucrose in the growth medium. Consistent with catabolite repression (CR), a DNA sequence with high homology to the CRE ( cis -active element) was identified upstream of the  aga  promoter. Sucrose-mediated CR depends on the phosphoenolpyruvate: sucrose phosphotransferase system (PTS) but is unaffected by a mutation in a gene encoding a homolog of the CRE regulatory protein CcpA.

Regulation of the α-Galactosidase Activity in Streptococcus pneumoniae: Characterization of the Raffinose Utilization System