Nature 531, 533–537 (2016); doi:10.1038/nature16993

In this Letter, we studied the three-dimensional structure of a protein from Mycobacterium smegmatis assigned as mycocerosic acid synthase (MAS) in sequence databases as A0R1E8 in Uniprot ( and YP_888986.1 in NCBI ( In conclusion, we provided a template structure of MAS-like polyketide synthases (PKSs) and a first example of reducing PKS architecture. However, we now note that Etienne et al.1 provided a biochemical characterization of a deletion strain of the corresponding gene MSMEG_4727 (, which indicated a physiological role of the protein in the production of 2,4-dimethyl-2-eicosenoic acid, a lipid component of lipooligosaccharides, rather than mycocerosic acids, via a reaction closely related to those of MAS. Until comprehensive characterization at the protein level is available, the protein we studied should therefore be referred to as a ‘mycocerosic-acid synthase like-PKS’ or ‘MAS-like PKS’; the database records will be updated accordingly. We thank the authors of ref. 1 for drawing our attention to this publication. The main scientific conclusions of our manuscript remain unchanged.