CHARACTERIZATION OF THE STREPTOCOCCUS-PNEUMONIAE MALTOSACCHARIDE REGULATOR MALR, A MEMBER OF THE LACI-GALR FAMILY OF REPRESSORS DISPLAYING DISTINCTIVE GENETIC FEATURES

The gene encoding a transcriptional repressor of the maltosaccharide u tilization operons of the Gram-positive bacterium Streptococcus pneumo niae (malR) has been cloned and sequenced. The genetic structure of th e locus reveals the presence of an upstream gene necessary for growth on maltotetraose medium (malA). The phenotype of malR- and malA- mutan ts obtained by interruption of the coding regions suggests that both g enes could belong to the same transcription unit. Two copies of a DNA motif consisting of three conserved regions of 59, 42, and 49 nucleoti des were found located upstream and downstream of the malA-malR putati ve operon. These DNA structures are almost identical to the reported B ox sequences associated with several genes of S. pneumoniae. The prote in encoded by malR was visualized and partially purified after selecti ve expression in Escherichia coli, whereas the product of malA was ide ntified in vitro. The amino acid sequence of MalR displays similaritie s with the Lac and Gal family of repressors. The highest similarities were found when comparing MalR with the E. coli Mall repressor, which is related with an indirect induction pathway of the maltose regulon. The significance of these similarities is discussed in terms of the po ssible evolutionary pathways followed by structural and regulatory gen es of sugar utilization systems in bacteria.