MODIFIED CROWTHER AND BLOW T-1 TRANSLATION FUNCTION FOR PARTIAL SEARCH MODELS

A simple modification to the fast T-1 translation function of Crowther & Blow [Crowther & Blow (1967). Acta Cryst. 23, 544-548] can reduce s ystematic error in cases where the input set of oriented search models represents a fraction of the scattering matter of the unknown crystal unit cell. The observed Patterson function is modified by a partial s elf-vector subtraction (SVS) and then the residual Patterson origin is removed In a test case where a protein/DNA complex crystal was search ed using a protein-only model, the highest signal-to-noise ratios for translation-search maps were obtained either with origin removal alone or partial SVS combined with origin removal. Origin removal is likely to be a generally useful alternative to SVS for the T-1 function.