yecS (Escherichia coli K12): ABC family putative inner membrane permease; Part of the ABC transporter complex FliY-YecC-YecS involved in L-cystine transport. The system can probably also transport L- cysteine, and it mediates accumulation of the toxic compounds L- selenaproline (SCA) and L-selenocystine (SeCys). Probably responsible for the translocation of the substrate across the membrane (Probable).