Elastic proteins are characterized by being able to undergo significant deformation, without rupture, before returning to their original state when the stress is removed. The sequences of elastic proteins contain elastomeric domains, which comprise repeated sequences, which in many cases appear to form beta-turns. In addition, the majority also contain domains that form intermolecular cross-links, which may be covalent or non-covalent. The mechanism of elasticity varies between the different proteins and appears to be related to the biological role of the protein.