Mediates nuclear encoded chloroplast preproteins binding to HSP90 prior to chloroplastic sorting (By similarity). Mediates the association of the molecular chaperones HSP70 and HSP90. Co-chaperone that forms a complex with HSP70 and HSP90 and preproteins (e.g. chloroplast preproteins) (By similarity). Interacts with HSP90. Expressed ubiquitously, with maximal expression in cotyledons, followed by shoots and flowers. By heat shock, heat, cold shock and wounding. The tetratricopeptide repeat (TPR) domain, forming a carboxylate clamp (CC), mediates interaction with the highly conserved 'EEVD' motif at the C-terminal ends of HSP90 and HSP70. Phosphorylated. Acetylated.