Function
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, probably via interactions with CasA, nicks target DNA and then unwinds and cleaves the target, leading to DNA degradation and invader neutralization. CasA is not required for formation of Cascade, but probably enhances binding to and subsequent recognition of both target dsDNA and ssDNA.
Sequence
MNLLIDNWIPVRPRNGGKVQIINLQSLYCSRDQWRLSLPRDDMELAALALLVCIGQIIAPAKDDVEFRHRIMNPLTEDEFQQLIAPWIDMFYLNHAEHPFMQTKGVKANDVTPMEKLLAGVSGATNCAFVNQPGQGEALCGGCTAIALFNQANQAPGFGGGFKSGLRGGTPVTTFVRGIDLRSTVLLNVLTLPRLQKQFPNESHTENQPTWIKPIKSNESIPASSIGFVRGLFWQPAHIELCDPIGIGKCSCCGQESNLRYTGFLKEKFTFTVNGLWPHPHSPCLVTVKKGEVEEKFLAFTTSAPSWTQISRVVVDKIIQNENGNRVAAVVNQFRNIAPQSPLELIMGGYRNNQASILERRHDVLMFNQGWQQYGNVINEIVTVGLGYKTALRKALYTFAEGFKNKDFKGAGVSVHETAERHFYRQSELLIPDVLANVNFSQADEVIADLRDKLHQLCEMLFNQSVAPYAHHPKLISTLALARATLYKHLRELKPQGGPSNG