DNA sequence-specific dimeric bisbenzimidazoles DBP(n) and DBPA(n) as inhibitors of H-NS silencing in bacterial cells

DNA sequence-specific fluorescent dimeric bisbenzimidazoles DBP(n) and DBPA(n), noncovalently interacting with A-T pairs in the minor groove of double-stranded DNA were used for studying and monitoring the expression of histone-like H-NS-dependent promoters. Histone-like H-NS selectively binds to AT-rich segments of DNA and silences a large number of genes in bacterial chromosomes. The H-NS-dependent promoters of Quorum Sensing (QS)-regulated lux operons of the marine bacteria mesophilic Aliivibrio fischeri, psychrophilic Aliivibrio logei were used. Escherichia colt lux biosensors were constructed by cloning fragments bearing QS-regulated promoters into the vector, thereby placing each fragment upstream of the promoterless Photorhabdus lurninescens luxCDABE genes. It was shown that the dimeric bisbenzimidazoles DBP(n) and DBPA(n) counteract the H-NS silencing activity. Thus, the presence of DBP(n) or DBPA(n) in the medium leads to an approximately 10-100-fold increase in the level of transcription of QS promoters in E. coli hns(+). The largest decrease in the level of H-NS repression was observed using ligands containing a linker with a length of ca. 18 angstrom, such as DBP(2) and DBPA(2). Ligands containing linkers with n = 1 and 3 are an order of magnitude less active; ligands with n = 4 are inactive. DBPA(2) exhibits activity starting with a concentration of 0.5 mu M; the minimum concentration of DBP (2) is 5-7 times higher. It is suggested that A-T pairs located at five nucleotide pair intervals, which correspond to the linker length in highly active ligands with n = 2, play a key role in the structure of H-NS-binding sites in QS-regulated promoters.