Expression of the gene encoding the major bacterial nucleotide protein H-NS is subject to transcriptional auto-repression.
Expression of a promoterless cat gene fused to a DNA fragment of approximately 400 bp, beginning at -313 of Escherichia coli hns, was significantly repressed in E. coli and Salmonella typhimurium strains with wild-type hns but not in mutants carrying hns alleles. CAT expression from fusions containing a shorter (110 bp) segment of hns was essentially unaffected in the same genetic backgrounds. The stage of growth was found to influence the extent of repression which was maximum (approximately 75%) in mid-log cultures and negligible in cells entering the stationary phase. The level of repression in early-log phase was lower than in mid-log phase cultures, probably because of the presence of high levels of Fis protein, which counteracts the H-NS inhibition by stimulating hns transcription. The effects observed in vivo were mirrored by similar results obtained in vitro upon addition of purified H-NS and Fis protein to transcriptional systems programmed with the same hns-cat fusions. Electrophoretic gel shift assays, DNase I footprinting and cyclic permutation gel analyses revealed that H-NS binds preferentially to the upstream region of its own gene recognizing two rather extended segments of DNA on both sides of a bend centred around -150. When these sites are filled by H-NS, an additional site between approximately -20 and -65, which partly overlaps the promoter, is also occupied. Binding of H-NS to this site is probably the ultimate cause of transcriptional auto-repression.
Falconi
M
M
Department of Biology, University of Camerino, Italy.
Higgins
N P
NP
Spurio
R
R
Pon
C L
CL
Gualerzi
C O
CO
D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D001426:Bacterial Proteins; D001483:Base Sequence; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D004755:Enterobacteriaceae / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D035021:Factor For Inversion Stimulation Protein; D015964:Gene Expression Regulation, Bacterial; D034982:Integration Host Factors; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015183:Restriction Mapping; D012486:Salmonella typhimurium / Q000235:genetics; D013329:Structure-Activity Relationship; D014158:Transcription, Genetic
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D035021:Factor For Inversion Stimulation Protein; C031908:H-NS protein, bacteria; D034982:Integration Host Factors; D011993:Recombinant Fusion Proteins; C440502:integration host factor, E coli