The role of the trehalose system in regulating the maltose regulon of Escherichia coli

The maltose regulon consists of 10 genes encoding an ABC transporter for ma ltose and maltodextrins as well as enzymes necessary for their degradation. MalK, the energy-transducing subunit of the transport system, acts phenoty pically as a repressor of MalT, the transcriptional activator of the mal ge nes. Using MacConkey maltose indicator plates we isolated an insertion muta tion that strongly reduced the repressing effect of overproduced MalK. The insertion had occurred in treR encoding the repressor of the trehalose syst em. The loss of TreR function led to derepression of treB encoding an enzym eII(Tre) of the PTS for trehalose and of treC encoding TreC, the cytoplasmi c trehalose-6-phosphate hydrolase. Further analysis revealed that maltose c an enter the cell by facilitated diffusion through enzymeII(Tre), thus caus ing induction of the maltose system. In addition, derepression of TreC by i tself caused induction of the maltose system, and a mutant lacking TreC was reduced in the uninduced level of mal gene expression indicating synthesis of endogenous inducer by TreC. Extracts containing TreC transformed [C-14] -maltose into another C-14-labelled compound (preliminarily identified as m altose 1-phosphate) that is likely to be an alternative inducer of the malt ose system.