EXPRESSION OF BACTERIAL GENES INVOLVED IN MALTOSE METABOLISM

Recent advances in the knowledge of the maltose regulons of enteric ba cteria have increased the number and complexity of factors involved bo th in gene expression and metabolite uptake by the cell. The transcrip tion activation performed by the MalT protein and the CRP-cAMP complex have been found to be connected with several regulation pathways impl icated in sugar transport and adaptation to changes in osmolarity in t he cell environment. In contrast to the positive regulation in enteric bacteria, the control of the maltose system in the Gram-positive bact erium Streptococcus pneumoniae may represent a more rudimentary scheme in which a classical repressor protein, MalR, regulates expression of the maltose operons. Considering the different mechanisms of transcri ption regulation proposed for these homologous systems, the maltose re gulon of S. pneumoniae appears to be specially useful as a model to st udy the changes that may have taken place, both in gene organization a nd control of gene expression, to lead to divergent mechanisms of tran scription regulation.