HOLOGRAPHIC METHODS IN CRYSTALLOGRAPHY. Abraham Szoke, Hanna Szoke Lawrence Livermore National Laboratory, Livermore, CA 94551 and John R. Somoza Dept. of Biochemistry and Biophysics, UC San Francisco, CA 94143

The holographic method is a novel method for generating electron density maps from crystallographic data. The advantage of this method over conventional Fourier maps is that it can easily take into account additional information and, in this process, it is capable of changing the phases of calculated reflections. Additional information includes: positivity of the electron density everywhere; near constancy of the electron density in the solvent region (similar to solvent flattening); a known part of the molecule (similar to molecular replacement); MIR; MAD and non-crystallographic symmetry. The program that implements the holographic method, EDEN, uses any and all these kinds of information simultaneously and consistently. We will present results of tests both on artificial examples and on real protein data. For example a model protein of 207 residues (Thaumatin) could be perfectly recovered from its last 47 residues (23% of the total) using a low resolution solvent mask that covers 1/2 of the volume of the unit cell. Results will be presented on studies of solvent structures and on MIR.

References: 1. Szoke, A. (1993) Acta Cryst. A49, 853-866. 2. Somoza, J. R., Szoke, H., Goodman, D. M., Beran, P., Truckses, D.,Kim, S-H. & Szoke, A. (1995) Acta Cryst. A51, 691-708. 145