CRISPR (clustered regularly interspaced short palindromic repeat), is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). CasE is required to process the pre-crRNA into single repeat-spacer units, with an 8-nt 5'-repeat DNA tag that may help other proteins recognize the crRNA. This subunit alone will cleave pre-crRNA, as will CasCDE or CasCE; cleavage does not require divalent metals or ATP. CasCDE alone is also able to form R-loops. Partially inhibits the cleavage of Holliday junctions by YgbT (Cas1). Yields a 5'-hydroxy group and a 2',3'-cyclic phosphate terminus. A component of Cascade, which participates in CRISPR interference, the third stage of CRISPR immunity. Cascade binds both crRNA and in a sequence-specific manner negatively supercoiled dsDNA target. This leads to the formation of an R-loop in which the crRNA binds the target DNA, displacing the noncomplementary strand. Cas3 is recruited to Cascade, nicks target DNA and then unwinds and cleaves the target, leading to DNA degradation and invader neutralization. Does not require a metal cofactor. Part of the Cascade ribonucleoprotein complex, with stoichiometry CasA(1),CasB(2),CasC(6),CasD(1),CasE(1)-crRNA(1). Interacts directly with crRNA, CasA, CasB and CasC. Stable subcomplexes of CasBCDE-crRNA and CasCDE-crRNA also form, both of which are able to bind target dsDNA, and CasCDE is able to form R-loops. CasCDE and CasCE complexes have endonuclease activity. Interacts with YgbT (Cas1). Binding of target ssRNA or dsDNA causes a conformational change in the Cascade complex. Repressed by H-NS, activated by LeuO. Activated by the BaeSR two-component regulatory system, possibly due to envelope stress. Part of the casABCDE-ygbT-ygbF operon. Loss of resistance to bacteriophage lambda infection, loss of plasmid silencing. Decreased levels of crRNA, increased levels of pre-crRNA, prevents pre-crRNA cleavage. Belongs to the CRISPR-associated protein Cas6/Cse3/CasE family. Subtype I-E/Ecoli subfamily.