[An improved rotational correlation method for the structure determination of biological macromolecules by averaging...

The averaging of electron micrographs of biological macromolecules by correlation techniques can be performed if the molecules lie plane to the support film. To improve the normal method which uses the autocorrelation function to determine the orientation of the molecules, a new method and its computer realization has been devised using iterative, translational and rotational correlations of the molecule images themselves. With this method the symmetry properties of yeast fatty acid synthetase have been studied. The results show: 1) The new method is very precise (angle accuracy ca. +/- 1 degrees). 2) Fatty acid synthetase contains a threefold rotation axis. A cyclic symmetry (C3) of the structure is likely. 3) The alpha-subunit consists of at least 2 protein domains.