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 b e involved in the utilization of a hitherto unknown carbohydrate which gene rates the intermediate L-xylulose. Transcription of yiaK-S as a single mess age from the unique promoter found upstream of yiaK: is proven in this stud y. The 5' end has been located at 60 bp upstream from the ATG. Expression o f the yiaK-S operon is controlled in the wild-type strain by a repressor en coded by yiaJ. No inducer molecule of the yiaK-S operon has been identified among over 80 carbohydrate or derivative compounds tested, the system bein g expressed only in a mutant strain lacking the YiaJ repressor. The lacZ tr anscriptional fusions in the genetic background of the mutant strain reveal ed that yiaK-S is modulated by the integration host factor and by the cycli c AMP (cAMP)-cAMP receptor protein (Crp) activator complex. A twofold incre ase in the induction was observed during anaerobic growth, which was indepe ndent of ArcA or Fnr. Gel mobility shift assays showed that the YiaJ repres sor 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 demonst rated that binding of cAMP-Crp to the Crp site 1, centered at -1.06, is ess ential for yiaK-S expression. The 5' end of the yiaJ gene was determined, a nd its promoter region was found to overlap with the divergent yiaK-S promo ter. Expression of yiaJ is autogenously regulated and reduced by the bindin g of Crp-cAMP to the Crp site 1 of the yiaK-S promoter.