On the use of low-resolution data for translation search in molecular replacement

Low-resolution reflections (approximately 15 A and lower) are very useful for the translation search in molecular replacement because they are less sensitive to model errors compared with the traditionally used reflections of resolution 4-10 A. At low resolution, however, the contribution from the bulk solvent is quite significant and corresponding structure factors calculated from a macromolecular model cannot be compared with experimental values if this contribution is neglected. The proposed method provides a way of fast translation searches where low-resolution reflections are taken into account. Test calculations using several experimental data sets show a dramatic improvement in the signal after the bulk-solvent correction and low-resolution reflections were included in the calculation; this improvement allowed unambiguous identification of the solution.