This study investigates a novel family of repetitive DNA sequences, referred to as clustered regularly interspaced short palindromic repeats (CRISPR), present in both archaeal and bacterial genomes but absent from eukaryotic and viral genomes. CRISPRs are characterized by direct repeats of 21-37 bp interspersed with non-repetitive spacer sequences. The presence of multiple CRISPR loci suggests that these elements are mobile. Four CRISPR-associated (cas) genes were identified, which are conserved in CRISPR-containing species but absent in CRISPR-negative species. The cas genes are adjacent to CRISPR loci, indicating a functional relationship. The cas3 gene contains motifs characteristic of helicases, and the cas4 gene shows motifs of the RecB family of exonucleases, suggesting roles in DNA metabolism or gene expression. The study also discusses the potential mechanisms of CRISPR spread, including lateral DNA transfer and transposition, and the possible functions of the Cas proteins. The biological significance of CRISPRs remains unclear, but they are associated with strain-dependent DNA polymorphism and may play a role in bacterial adaptation and evolution.This study investigates a novel family of repetitive DNA sequences, referred to as clustered regularly interspaced short palindromic repeats (CRISPR), present in both archaeal and bacterial genomes but absent from eukaryotic and viral genomes. CRISPRs are characterized by direct repeats of 21-37 bp interspersed with non-repetitive spacer sequences. The presence of multiple CRISPR loci suggests that these elements are mobile. Four CRISPR-associated (cas) genes were identified, which are conserved in CRISPR-containing species but absent in CRISPR-negative species. The cas genes are adjacent to CRISPR loci, indicating a functional relationship. The cas3 gene contains motifs characteristic of helicases, and the cas4 gene shows motifs of the RecB family of exonucleases, suggesting roles in DNA metabolism or gene expression. The study also discusses the potential mechanisms of CRISPR spread, including lateral DNA transfer and transposition, and the possible functions of the Cas proteins. The biological significance of CRISPRs remains unclear, but they are associated with strain-dependent DNA polymorphism and may play a role in bacterial adaptation and evolution.