The promoter of the tgt/sec operon in Escherichia coli is preceded by an upstream activation sequence that contains a high affinity FIS binding site

摘要

The tgt/sec operon in E.coll consists of five genes: queA, tgt, ORF12, SecD, and SecF. QueA and Tgt participate in the biosynthesis of the hypermodifled t-RNA nucleoside Queuosine, whereas SecD and SecF are involved in protein secretion. Examination of the promoter region of the operon showed structural similarity to promoter regions of the rrn-operons. An upstream activation sequence (UAS) containing a potential binding site for the factor of inversion stimulation (FIS) was found. Gel retardation assays and DNasel footprinting Indicated, that FIS binds specifically and with high affinity to a site centred at position ?58. Binding of FIS caused bending of the DNA, as deduced from circular permutation analysis. Various 5′ deletion mutants of the promoter region were constructed and fused to a lacZ reporter gene to determine the influence of the UAS element on the promoter strength. An approximately two-fold activation of the promoter by the UAS element was observed.