USE OF GENE FUSIONS TO STUDY THE EXPRESSION OF MALT THE POSITIVE REGULATOR GENE OF THE MALTOSE REGULON

The technique of Casadaban was adapted to the selection of Escherichia coli strains in which lacZ is fused to malT, the positive regulator gene of the maltose regulon. Genetic evidence is presented that each of these strains codes for a malT-lacZ hybrid protein, which is endowed with .beta.-galatosidase activity. The procedure used to characterize the fusion strains also allows the establishment of the direction of malT transcription, which is clockwise on the circular genetic map of E. coli. From the results regarding the expression of the malT-lacZ hybrid genes in the fusion strains it is concluded that the expression of malT, like that of araC in the L-arabinose system, is sensitive to catabolite repression but that, unlike that of araC, it is not autoregulated.