Mutations in the promoter regions of the malEFG and malK-lamB operons of Escherichia coli K12.

The malB region of Escherichia coli is composed of two operons, malEFG and malK-lamB, transcribed divergently from a control region located between the malE and malK genes. Expression of the malB operons is under the positive control of the malT gene product (MalT) and maltose and of the crp gene product (CRP) and cyclic AMP. Strains in which the lac genes have been fused to malE or malK are unable to use lactose as carbon source if they have been deleted for malT or crp. Mutations in the malB region allowing such fusion strains to grow on lactose have been isolated. These and previously isolated mutations were genetically characterized. As regards the malEp promoter mutations, malEp9, malEp1 and malEp6 create new promoters that are MalT and CRP independent. malEp9 and malEp1 change residues -1 and -2, respectively, of malEp without altering its activity. malEp6 duplicates six base-pairs between residues -22 and -23. malEp3 improves the -10 region hexamer. malEp5 deletes residues -29 to -62. It creates a new promoter that is MalT independent, CRP dependent, likely by fusing together functional regions of malEp that are normally apart. malEp5 also reduces the expression of malK-lamB, suggesting the existence of a link between the malEp and malKp promoters. As regards the malKp mutations, malKp6 changes residue -81 of malKp without altering its activity. It creates a new promoter, which is MalT independent, CRP dependent, likely by using a pre-existing cyclic AMP/CRP binding site. malKp102 changes residue -36, two bases upstream of the -35 region hexamer. It decreases the activity of malKp by at least four orders of magnitude and likely alters the MalT binding site. These results are discussed in terms of regulatory interactions within the malB control region.