MalR-mediated regulation of the Streptococcus pneumoniae malMP operon at promoter P-M - Influence of a proximal divergent promoter region and competition between MalR and RNA polymerase proteins

The Streptococcus pneumoniae mal regulon contains two operons, malXCD and m alMP involved in the uptake and utilization of maltosaccharides. Both opero ns are transcribed from two divergent promoters, P-X and P-M, and are negat ively regulated by the MalR transcriptional repressor. Purified MalR protei n binds to two DNA regions that encompasses both promoters, thus occupying its two operators, O-M and O-X. However, the levels of occupation and repre ssion were different, being higher when MalR was bound to O-M than when it was anchored to O-X. Competition experiments between MalR and the Escherich ia coli RNA polymerase on promoters P-M and P-X showed that the affinity of either protein for the promoter/operator DNA sequences was important to de termine the frequency of transcription initiation. In addition to the contr ol exerted by MalR, expression from promoter P-M was affected by upstream s equences located within or close to P-X promoter.