Recently, considerable insight has been gained into the modular organizatio
n of nonribosomal peptide synthetases (NRPS). The three-dimensional structu
res of domains associated with substrate adenylation and covalent binding h
ave been solved as well as the structure of a priming enzyme required for t
he post-translational modification of NRPS. Taken together, these studies w
ill help us to understand the architecture of these mega-enzymes.