Provided are amino acid sequences capable of binding to and inhibiting a Cas protein's ability to bind to a nucleic acid molecule, thereby inhibiting the Cas protein's function in genome editing. Such Cas protein inhibitors, which can be comprised of a major coat protein (G8P), an extracellular region of the G8P (G8P.sub.EX), or a biological equivalent, are useful in improving the specificity of Cas protein-based genome editing procedures.

Provided are amino acid sequences capable of binding to and inhibiting a Cas protein's ability to bind to a nucleic acid molecule, thereby inhibiting the Cas protein's function in genome editing. Such Cas protein inhibitors, which can be comprised of a major coat protein (G8P), an extracellular region of the G8P (G8P.sub.EX), or a biological equivalent, are useful in improving the specificity of Cas protein-based genome editing procedures.