Regulation of expression of the yiaKLMNOPQRS operon for carbohydrate utilization in Escherichia coli:: Involvement of the main transcriptional factors

The yiaKLMNOPQPS (yiaK-S) gene cluster of Escherichia coli is believed to be involved in the utilization of a hitherto unknown carbohydrate which generates the intermediate L-xylulose. Transcription of yiaK-S as a single message from the unique promoter found upstream of yiaK: is proven in this study. The 5' end has been located at 60 bp upstream from the ATG. Expression of the yiaK-S operon is controlled in the wild-type strain by a repressor encoded by yiaJ. No inducer molecule of the yiaK-S operon has been identified among over 80 carbohydrate or derivative compounds tested, the system being expressed only in a mutant strain lacking the YiaJ repressor. The lacZ transcriptional fusions in the genetic background of the mutant strain revealed that yiaK-S is modulated by the integration host factor and by the cyclic AMP (cAMP)-cAMP receptor protein (Crp) activator complex. A twofold increase in the induction was observed during anaerobic growth, which was independent of ArcA or Fnr. Gel mobility shift assays showed that the YiaJ repressor binds to a promoter fragment extending from -50 to +121. These studies also showed that the cAMP-Crp complex can bind to two different sites. The lacZ transcriptional fusions of different fragments of the promoter demonstrated that binding of cAMP-Crp to the Crp site 1, centered at -1.06, is essential for yiaK-S expression. The 5' end of the yiaJ gene was determined, and its promoter region was found to overlap with the divergent yiaK-S promoter. Expression of yiaJ is autogenously regulated and reduced by the binding of Crp-cAMP to the Crp site 1 of the yiaK-S promoter.