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

10 p.-7 fig.-1 tab.The Streptococcus pneumoniae malregulon contains two operons, malXCD andmalMP involved in the uptake and utilization of maltosaccharides. Both operons are transcribed from two divergent promoters, PX andPM , and are negatively regulated by the MalR transcriptional repressor. Purified MalR protein binds to two DNA regions that encompasses both promoters, thus occupying its two operators, OM and OX. However, the levels of occupation and repression were different, being higher when MalR was bound to OM than when it was anchored to OX. Competition experiments between MalR and the Escherichia coli RNA polymerase on promoters PM andPX showed that the affinity of either protein for the promoter/operator DNA sequences was important to determine the frequency of transcription initiation. In addition to the control exerted by MalR, expression from promoter PM was affected by upstream sequences located within or close toPX promoter.This work was supported by Comisión Interministerial de Ciencia y Tecnología Grant BMC2000-0550, by Comunidad Autónoma de Madrid Grant 07B/30/99, and by the Program for Strategic Groups.Peer reviewe