Expression of bacterial genes involved in maltose metabolism.

Recent advances in the knowledge of the maltose regulons of enteric bacteria have increased the number and complexity of factors involved both in gene expression and metabolite uptake by the cell. The transcription activation performed by the MalT protein and the CRP-cAMP complex have been found to be connected with several regulation pathways implicated in sugar transport and adaptation ot changes in osmolarity in the cell environment. In contrast to the positive regulation in enteric bacteria, the control of the maltose system in the Gram-positive bacterium 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 transcription regulation proposed for these homologous systems, the maltose regulon of S. pneumoniae appears to be specially useful as a model to study the changes that may have taken place, both in gene organization and control of gene expression, to lead to divergent mechanisms of transcription regulation.