Together with HP30-1 and HP30-2, triggers the import and insertion of transit sequence-less multi-pass transmembrane proteins (e.g. CEQORH) into the chloroplastic inner membrane. Homodimer. Probable component of a protein-conducting channel made of HP30-1, HP30-2 and HP20 that mediates the import of transit sequence-less proteins into the chloroplastic inner membrane. Interacts with CEQORH. Expressed in young cotyledons, roots, leaves and flowers. Peak of expression during cotyledon development. Impaired import of CEQORH in chloroplast inner membranes. Belongs to the Tim17/Tim22/Tim23 family.