Qian, Y. Q.Billeter, M.Otting, G.Müller, M.Gehring, W. J.Wüthrich, K.2026-03-012026-03-010092-8674PubMed:2572329ORCID:/0000-0002-0563-0146/work/206892067https://hdl.handle.net/1885/733806851The structure of the Antennapedia homeodomain from Drosophila melanogaster was determined by nuclear magnetic resonance spectroscopy in solution. It includes three well-defined helices (residues 10-21, 28-38, and 42-52) and a more flexible fourth helix (residues 53-59). Residues 30-50 form a helix-turn-helix motif virtually identical to those observed in various prokaryotic repressors. Further comparisons of the homeodomain with prokaryotic repressors showed that there are also significant differences in the molecular architectures. Overall, these studies support the view that the third helix of the homeodomain may function as the DNA recognition site. The elongation of the third helix by the fourth helix is a structural element that so far appears to be unique to the Antennapedia homeodomain.We thank Dr. S. Harrison for the coordinates of 434 repressor residues l-89, Mr. T. H. Xia for help with the picture display, and Mrs. E. Huber and Mr. R. Marani for the careful processing of the typescript. Financial support by the Schweizerischer Nationalfonds (projects 31.2517488 and K 03613.87) and the use of the Cray X-MP/28 of the ETH Ziirich are gratefully acknowledged.8en1989-11-0310.1016/0092-8674(89)90040-80024407460