Beschreibung:
<jats:title>Summary</jats:title><jats:p>Inheritable bacterial defence systems against phage infection and foreign DNA, termed CRISPR (<jats:italic><jats:bold>c</jats:bold>lustered <jats:bold>r</jats:bold>egularly <jats:bold>i</jats:bold>nterspaced <jats:bold>s</jats:bold>hort <jats:bold>p</jats:bold>alindromic <jats:bold>r</jats:bold>epeats</jats:italic>), consist of <jats:italic>cas</jats:italic> protein genes and repeat arrays interspaced with sequences originating from invaders. The Cas proteins together with processed small spacer‐repeat transcripts (crRNAs) cause degradation of penetrated foreign DNA by unknown mechanisms. Here, we have characterized previously unidentified promoters of the <jats:italic>Escherichia coli</jats:italic> CRISPR arrays and <jats:italic>cas</jats:italic> protein genes. Transcription of precursor crRNA is directed by a promoter located within the CRISPR leader. A second promoter, directing <jats:italic>cas</jats:italic> gene transcription, is located upstream of the genes encoding proteins of the Cascade complex. Furthermore, we demonstrate that the DNA‐binding protein H‐NS is involved in silencing the CRISPR‐<jats:italic>cas</jats:italic> promoters, resulting in cryptic Cas protein expression. Our results demonstrate an active involvement of H‐NS in the induction of the CRISPR‐<jats:italic>cas</jats:italic> system and suggest a potential link between two prokaryotic defence systems against foreign DNA.</jats:p>