ε-Poly-L-lysine (ε-PL) consists of 25-35 L-lysine residues in isopeptide linkages and is one of only two amino acid homopelymers known in nature.Elucidating the biosynthetic mechanism of ε-PL should open new avenues for creating novel classes of biopolymers.We have recently reported the purification of an ε-PL synthetase (Pls:130 kDa) and the cloning of its gene from an ε -PL producing strain of Streptomyces albulus [1].Pls was found to be a membrane protein with adenylation and thiolation domains characteristic of the nonribosomal peptide synthetases (NRPSs).