Temperature-sensitive catabolite activator protein in Escherichia coli BUG6.

BUG6 is a temperature-sensitive cell division mutant which forms filaments at the nonpermissive temperature. Synthesis of the maltose- and galactose-binding protein-dependent transport systems is also temperature sensitive in BUG6. Using operon and protein fusions of the maltose transport genes to lacZ, we observed that the temperature-sensitive control of the maltose transport system in BUG6 occurs at the transcriptional level. By P1-mediated transductions, we found that BUG6 contains two independent temperature-sensitive mutations. One maps between 2 and 3 min on the Escherichia coli linkage map, in close proximity to the fts-envA region. This mutation is responsible for temperature-sensitive cell division. The other mutation maps at 73 min in crp, the structural gene of the catabolite activator protein. The latter could be complemented by a hybrid plasmid carrying the wild-type crp as the only gene on a 0.9-kilobase HindIII-AluI restriction fragment. The mutation in crp alone was found to be responsible for the temperature-sensitive synthesis of the maltose transport system. Although it causes a complete block of transcription of the maltose transport genes at 41 degrees C, this mutation had only a marginal effect on the transcription of the lac operon.