title: Target motifs affecting natural immunity by a constitutive CRISPR-Cas system in Escherichia coli.
abstract: Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR associated (cas) genes conform the CRISPR-Cas systems of various bacteria and archaea and produce degradation of invading nucleic acids containing sequences (protospacers) that are complementary to repeat intervening spacers. It has been demonstrated that the base sequence identity of a protospacer with the cognate spacer and the presence of a protospacer adjacent motif (PAM) influence CRISPR-mediated interference efficiency. By using an original transformation assay with plasmids targeted by a resident spacer here we show that natural CRISPR-mediated immunity against invading DNA occurs in wild type Escherichia coli. Unexpectedly, the strongest activity is observed with protospacer adjoining nucleotides (interference motifs) that differ from the PAM both in sequence and location. Hence, our results document for the first time native CRISPR activity in E. coli and demonstrate that positions next to the PAM in invading DNA influence their recognition and degradation by these prokaryotic immune systems.
authors.affiliation: Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain.
authors.forename: Cristóbal
authors.initials: C
authors.lastname: Almendros
authors.forename: Noemí M
authors.initials: NM
authors.lastname: Guzmán
authors.forename: César
authors.initials: C
authors.lastname: Díez-Villaseñor
authors.forename: Jesús
authors.initials: J
authors.lastname: García-Martínez
authors.forename: Francisco J M
authors.initials: FJ
authors.lastname: Mojica
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000276:immunology*; D029968:Escherichia coli Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D023061:Gene Order; D055029:Inverted Repeat Sequences; D008969:Molecular Sequence Data; D059372:Nucleotide Motifs; D010957:Plasmids / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins