9.B.111 The 6 TMS Lysyl tRNA Synthetase (LysS) Family
Several lysyl tRNA and alanyl synthetases of the tRNA ligase 2 family, include a 6 TMS segment that appears to correspond to the second 6 TMS unit in certain MFS permeases of the DHA2 family (TC# 2.A.1.3). Two such proteins from Streptomyces coelicolor (O69916 and Q9X8H7) show sequence similarity to the proteobacterial MFS permeases. The regions of sequence similarity are TMSs 2-5 in the former protein aligning with TMSs 2-5 in the second half of the latter proteins. This hydrophobic second 6 TMS unit in the domain in LysS may have derived from the second half of an MFS permease. It is not known if it has transport function. However, many tRNA synthetases have N-terminal or central MFS domains.