Molecular Mechanisms of Type I CRISPR-Cas Systems

CRISPR-Cas class 1 includes types I, III, and IV. All class 1 systems have typical multisubunit complexes, often with a Cas nuclease, either stand-alone (Cas3 in type I) or tightly associated with the Cascade-like complex (Cas10 in type III) or tightly associated with the Cascade-like complex (Cas10 in type III). Many fundamental discoveries of relevant details of the CRISPR-Cas mechanism have been described in a series of seminal studies of type I CRISPR-Cas systems. This chapter discusses the key discoveries and relevant mechanistic features, and recently established applications of type I complexes. To test the in vivo role of the Cascade complex in antiviral defense, the complex was coexpressed with a designed CRISPR, resulting in mature crRNA guides with spacer sequences complementary to gene fragments of phage lambda.