A series of Escherichia coli strains in which the lacZ gene is fused to any of the three maltose operons were previously isolated (Silhavy et al, 1976, 1977). Starting from one such strain, in which β-galactosidase synthesis is induced by maltose, mutants could be selected which synthesize this enzyme constitutively. Several of these mutants carry a mutation in malT, the positive regulator gene of the maltose system. The mutations, called malTc, are both cis and trans dominant over wild type. The failure of the malT+ product to repress the constitutive expression resulting either from a malTc mutation (this paper) or from initiator constitutive mutations (Hofnung & Schwartz 1971) strongly suggests that, in contrast to the l-arabinose system, the maltose system is regulated in a strictly positive manner.
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology