Structural dissection and functional analysis of the complex promoter of the streptokinase gene from Streptococcus equisimilis H46A

The overlapping tandem promoters of the streptokinase gene, P1 and P2, identified previously by S1 nuclease transcript mapping were functionally dissected by mutagenesis of their -10 regions and fused transcriptionally with or without the 202-bp upstream region (USR) to the luciferase reporter gene (luc) from Photinus pyralis to analyze the contribution of the different sequence elements to promoter activity in Escherichia coli and the homologous Streptococcus equisimilis strain H46A. In E. coli, virtually the entire promoter activity derived from the upstream promoter F1. In S. equisimilis, luc expression increased in the following order of the involved sequence elements: P2 congruent to P2+USR<P1<P1+P2<P1+USR<P1+P2+USR. This shows that (1) in the homologous system, P1 and P2 alone are extremely weak, (2) in the USR-less arrangement, only the combined core promoters have substantial activity, and (3) the USR stimulates only P1 and the combination of P1+P2. Thus, the tandem promoters presumably function by mutual contributary action and their full activity strongly depends on the AT-rich and statically bent upstream region. The distinctive feature determining the strength of P1 in both hosts appears to be its extended -10 region which matches the consensus TRTGN established for strong S. pneumoniae and Bacillus subtilis promoters.