Proteins directed to the thylakoids carry sub-organellar targeting signals in addition to the transit signal. Thylakoid protein sorting occurs by distinct pathways: the chloroplast secretory or cpSec pathway, the chloroplast twin-arginine or cpTat pathway, and the chloroplast signal recognition particle, or cpSRP pathway. The cpSec pathway translocates unfolded precursors to the thylakoid lumen using an ATP-dependent cpSecA motor protein which pulls the peptides through the cpSecY channel. In the cpTAT pathway, twin-arginine residues of the thylakoid signal sequences induce oligomerization of Tat proteins to form a pore-like complex. Folded proteins are translocated across these Tat pores into the thylakoid lumen using the electrochemical potential of the proton gradient across the thylakoid membrane. The cpSRP pathway translocates unfolded proteins utilizing the energy of GTP hydrolysis through a cpSRP translocase, a Sec family protein.