A modified ACORN to solve protein structures at resolutions of 1.7 A or better.

ACORN has previously been shown to provide an efficient density-modification procedure for the solution of protein structures using diffraction data to better than 1.3 A. The initial phase set could be obtained from a variety of sources such as the position of a heavy atom, a set of scatterers such as S that had been positioned from anomalous dispersion measurements, a fragment or a very low homology model placed from a molecular-replacement search.

ACORN in CCP4 and its applications.

ACORN is a comprehensive and efficient phasing procedure for the determination of protein structures when atomic resolution data are available. Reliable phases can be developed from a fragment composed of a small percentage (less than 5%) of the scattering matter of the unit cell. For example, ACORN has been used to solve a structure of 1093 atoms from only one S atom.