.. _subs_buildtasks_cleave: cleave ------ A ``cleave`` task is used to cleave one or more chains in a system. A ``cleave`` task requires a single ``sites`` subdirective which contains a list of cleavage site desigations. The format for a cleavage site designation is: ``:-`` ```` is the chain ID, ```` and ```` are the residue numbers (including optionally appended insertion codes) of the two residues that form the peptide bond. For example, ``A:12-15`` would create a cleavage between residue 12 and residue 15 in chain A. When a cleavage occurs, all residues in the parent chain N-terminal to the cleavage site retain their original chain ID, while those residues C-terminal to the cleavage site are assigned the first new available chain ID. An example of a ``cleave`` task is shown in :ref:`example sars cov2 spike ba2`.