NEW TECHNIQUES FOR APPLYING ANOMALOUS-SCATTERING AND ISOMORPHOUS-REPLACEMENT DATA INCORPORATED IN ANOMIR - A GENERAL APPLICATION PACKAGE

A computer package ANOMIR is described which can derive phases from an omalous scattering and/or isomorphous-replacement data in any combinat ion. For anomalous scattering it incorporates five methods of applying one-wavelength data and three methods for multiple-wavelength data in cluding SPIN, reported here for the first time. In addition there are three procedures for multiple-wavelength data - the first modifying da ta for different wavelengths to make them mutually consistent, the sec ond estimating the contributions of the anomalous scatterers alone and the third which rinds anomalous differences. For single isomorphous r eplacement or one-wavelength anomalous scattering the phase ambiguity can be resolved by the direct method [Fan, Han, Qian & Yao (1984). Act a Cryst. A40, 489-495] but for multiple isomorphous replacement the ma in method is an adaptation of the probability-curve method [Blow & Cri ck (1959). Acta Cryst. 12, 794-802]. A new statistical method is descr ibed for estimating the standard error in measuring magnitudes which i s independent of having subsets of centric reflections. A method is de scribed whereby the weights associated with phase estimates are used t o generate probability curves, through which it is possible to combine estimates from different methods and to produce a 'best phase' and fi gure-of-merit for every reflection. ANOMIR procedures are also availab le for handling combinations of one-wavelength anomalous scattering wi th single-or multiple-isomorphous replacement. A final process, which is always beneficial, is a single parallel application of the tangent formula. The ANOMIR package has been designed for easy use and is cont rolled throughout by KEYWORDS. Results for several structures are give n and compared with those found from the MLPHARE program in the CCP4 p ackage.