The amino-terminal domain of influenza A virus matrix protein (residues 1-164) was crystallized at pH 7 into a new crystal form in space group P1. This packing of the protein implies that M1(1-164) was monomeric in solution when it crystallized. Otherwise, the structure of the M1 fragment in the pH 7 crystals was the same as the monomers in crystals formed at pH 4 where crystal packing resulted in dimer formation [B. Sha and M. Luo, 1997, Nature Struct. Biol. 4, 239-244]. Analysis of intact M1 protein, the N-terminal domain, and the remaining C-terminal fragment (residues 165-252) in solution also showed that the N-terminal domain was monomeric with the same dimensions as determined from the crystal structure. Intact M1 protein was also monomeric but with an elongated shape due to the presence of the C-terminal part. Circular dichroism showed that the C-terminal part of M1 contained helical structure. A model for soluble M1 is presented, based on the assumption that the C-terminal domain is spherical, in which the N- and C-terminal domains are connected by a linker sequence which is available for proteolytic attack.

The outstanding property of glutamate synthase is the ability to coordinate the activity of its various functional sites to avoid wasteful consumption of L-glutamine. The structure reveals two polypeptide segments that connect the catalytic centers and embed the ammonia tunnel, thus being ideally suited to function in interdomain signaling. Depending on the enzyme redox and ligation states, these signal-transducing elements may affect the active site geometry and control ammonia diffusion through a gating mechanism.

A new program in the Daresbury Laue software suite has been developed for the scaling and normalization of Laue intensity data, to yield fully corrected structure amplitudes. Previously available routines have been improved, and additional options for re®nement, control and statistical diagnostic output provided. A new feature, namely a wavelength-and positiondependent absorption correction that models a twodimensional surface derived from the Laue data alone, is discussed in detail; it is tested on simulated and real data, and the improvement in data quality is demonstrated. The wavelength normalization function is now able, when suf®-ciently redundant experimental data are available, to model ®ne details such as the features arising from the modi®cation of the incident intensity spectrum by a platinum mirror in the beamline optics. A full data set for tetragonal lysozyme is processed with the new program, and extensive statistical output is given.

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