Together with the chaperonin GroEL, plays an essential role in assisting protein folding. The GroEL-GroES system forms a nano-cage that allows encapsulation of the non-native substrate proteins and provides a physical environment optimized to promote and accelerate protein folding. GroES binds to the apical surface of the GroEL ring, thereby capping the opening of the GroEL channel. Heptamer of 7 subunits arranged in a domed ring (Ref.11, PubMed:12837792). 2 rings join in their base to form a spherical cage-like structure; both heptamers and tetradecamers exist in solution (PubMed:12837792). Interacts with RimI (PubMed:27353550). Induced in response to heat shock (45 degrees Celsius), pH 4, pH 10, ethanol, H(2)O(2), hyperosmolarity and starvation (PubMed:18227175). N-terminus is acetylated by RimI. Essential, it cannot be deleted. Belongs to the GroES chaperonin family.