Involved in protein precursor import into chloroplasts. Part of the motor complex consisting of a co-chaperone (TIC40) and a chaperone (HSP93) associated with the import channel (TIC110). Causes the release of bound transit peptides from TIC110 and stimulates ATP hydrolysis by HSP93. Involved in reinsertion of proteins from the chloroplast stroma into the inner membrane. Part of the Tic complex. Interacts with HSP93, TIC110, TIC62 and TOC75. Down-regulated by cold stress. The STI1 2 domain (373-412) has a stimulatory effect on HSP93 ATP hydrolysis. Inserts into the inner envelope membrane from the stroma after import from the cytoplasm. The transit peptide undergoes a two-step processing. The initial cleavage to generate the intermediate found in the stroma is mediated by the stromal processing peptidase (SPP) while the final processing step by a signal peptidase I-type (SPase I), possibly PLSP1, requires association with the inner membrane.