Functional CRISPR-Cas systems provide many bacteria and most archaea with adaptive immunity against invading DNA elements. CRISPR arrays store DNA fragments of previous infections while products of cas genes provide immunity by integrating new DNA fragments and using this information to recognize and destroy invading DNA. Escherichia coli contains the CRISPR-Cas type I-E system in which foreign DNA targets are recognized by Cascade, a crRNA-guided complex comprising five proteins (CasA, CasB, CasC, CasD, CasE), and degraded by Cas3. In E. coli the CRISPR-Cas type I-E system is repressed by the histone-like nucleoid-structuring protein H-NS. H-NS repression can be relieved either by inactivation of the hns gene or by elevated levels of the H-NS antagonist LeuO, which induces higher transcript levels of cas genes than was observed for Δ hns cells. This suggests that derepression in Δ hns cells is incomplete and that an additional repressor could be involved in the silencing. One such candidate is the H-NS paralog protein StpA, which has DNA binding preferences similar to those of H-NS. Here we show that overexpression of StpA in Δ hns cells containing anti-lambda spacers abolishes resistance to λ vir infection and reduces transcription of the casA gene. In cells lacking hns and stpA genes, the transcript levels of the casA gene are higher than Δ hns and similar to wt cells overexpressing LeuO. Taken together, these results suggest that Cascade genes in E. coli are repressed by the StpA protein when H-NS is absent. Image 1 • Ectopic expression of StpA abolishes CRISPR-Cas mediated resistance to phage infection in cells lacking H-NS. • Chromosomal expression of StpA partially represses expression from the P cas8e promoter in Δ hns cells. • CRISPR-Cas mediated resistance to λ vir phage infection in leuO -expressing cells is temperature-dependent. [ABSTRACT FROM AUTHOR]