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. The map from ACORN typically reveals the 90% of whole structure. The initial model can be automatically built using ARP/wARP or QUANTA. ACORN can also be used to determine substructures of heavy atoms or anomalously scattering atoms from SAD or MAD data at much lower resolutions such as 3.5 A. Some test results of using ACORN on known structures are presented here. ACORN has solved four new protein structures by users in the UK and France, and some results kindly provided by them are described in this paper.