The ATP-dependent protease Ti(Clp) consists of two different multimeric components: ClpA containing ATP-cleaving sites and ClpP, with serine active sites for proteolysis. Here we summarize the most recent results on the structure and function of protease Ti. (1) The clpA gene has dual translational initiation sites and therefore encodes two polypeptides with sizes of 84 and 65 kDa. The abbreviated form of ClpA may play an important role in regulation of the ATP-dependent proteolysis, since it inhibits the ability of the 84-kDa ClpA in supporting the ClpP-mediated protein breakdown and the autodegradation of the 84-kDa ClpA. (2) ClpA contains two highly conserved sequences for ATP-binding: the first site is essential for oligomerization and the second site is responsible for ATP hydrolysis. (3) ATP hydrolysis by ClpA is required not only for assembly of the ClpA/ClpP complex but also for its rapid dissociation.