Threonyl-tRNA Synthetase is a member of the aminoacyl-tRNA synthetase family， key enzymes of protein biosynthesis which charge tRNA molecules with the respective amino acids. This 83 kDa protein is an autoantigen recognized by PL-7 antibodies which occur in a subset of patients with polymyositis and dermatomyositis. Preliminary data suggest that PL-7 antibodies（similar to Jo-1 antibodies) indicate an increased risk for lung involvement， but this needs to be confirmed for a larger number of cases.
