CRYSTALLOGRAPHY AND NMR SYSTEM - A NEW SOFTWARE SUITE FOR MACROMOLECULAR STRUCTURE DETERMINATION

A new software suite, called Crystallography & NMR System (CNS), has b een developed for macromolecular structure determination by X-ray crys tallography or solution nuclear magnetic resonance (NMR) spectroscopy. In contrast to existing structure-determination programs the architec ture of CNS is highly flexible, allowing for extension to other struct ure - determination methods, such as electron microscopy and solid-sta te NMR spectroscopy. CNS has a hierarchical structure: a high-level hy pertext markup language (HTML) user interface, task-oriented user inpu t files, module files, a symbolic structure-determination language (CN S language), and low-level source code. Each layer is accessible to th e user. The novice user may just use the HTML interface, while the mor e advanced user may use any of the other layers. The source code will be distributed, thus source-code modification is possible. The CNS lan guage is sufficiently powerful and flexible that many new algorithms c an be easily implemented in the CNS language without changes to the so urce code. The CNS language allows the user to perform operations on d ata structures, such as structure factors, electron-density maps, and atomic properties. The power of the CNS language has been demonstrated by the implementation of a comprehensive set of crystallographic proc edures for phasing, density modification and refinement. User-friendly task-oriented input files are available for nearly all aspects of mac romolecular structure determination by X-ray crystallography and solut ion NMR.