H-NS AND STPA PROTEINS STIMULATE EXPRESSION OF THE MALTOSE REGULON INESCHERICHIA-COLI

The nucleoid-associated protein H-NS is a major component of the chrom osome-protein complex, and it is known to influence the regulation of many genes in Escherichia coli. Its rule in gene regulation is manifes ted by the increased expression of several gene products in hns mutant strains. Here we report findings showing that H-NS and the largely ho mologous protein StpA play a positive role in the expression of genes in the maltose regulon, In studies with hns mutant strains and derivat ives also deficient in the stpA gene, we found that expression of the LamB porin was decreased, Our results showed that the amounts of both LamB protein and lamB mRNA were greatly reduced in hns and hns-stpA mu tant strains. The same results were obtained when we monitored the amo unt of transcription from the malEFG operon, The lamB gene is situated in the malKlamBmalM operon, which forms a divergent operon complex to gether with the malEFG operon, The activation of these genes depends o n the action of the maltose regulon activator MalT and the global acti vator cyclic AMP receptor protein. Using a malT-lacZ translational fus ion and antiserum raised against MalT to measure the expression of Mal T, we detected reduced MalT expression in hns and hns-stpA mutant stra ins in comparison with the wild-type strain, Our results suggest that the H-NS and StpA proteins stimulate MalT translation and hence play a positive role in the control of the maltose regulon.