THE MALTOSE MALTODEXTRIN REGULON OF STREPTOCOCCUS-PNEUMONIAE - DIFFERENTIAL PROMOTER REGULATION BY THE TRANSCRIPTIONAL REPRESSOR MALR/

The Streptococcus pneumoniae MalR protein regulates the transcription of two divergent operons, malXCD and malMP, involved in maltosaccharid e uptake and utilization, respectively. MalR belongs to the LacI-GalR family of transcription repressors. The protein binds specifically to two operator sequences in the intergenic region between these operons. The affinity of MalR for the malMP binding sequence is higher than fo r the malXCD site. Results obtained in vivo using transcriptional fusi ons with reporter genes indicate low repression level of malXCD by Mal R when compared with malMP. This behavior may be correlated with the e xistence of separate induction pathways for maltose, maltotriose, and maltotetraose. The similarities found at the operator sequences and bi nding domains for MalR and enterococcal repressor proteins suggest tha t the pneumococcal maltosaccharide regulation system is closely relate d to several Gram-negative metabolic pathways, but not to the structur ally similar Escherichia coli maltose regulon.