Electron microscopic studies on the arrangements of hexon polypeptides in a two-dimensional crystalline array

Two distinct profiles of hexon end parts were detected in two-dimensional adenovirus hexon crystalline arrays: (i) hexons displaying three approximately oblong subunits around a triangular hole, and (ii) triangular hexons showing three main subunits with Y-shaped slits in their centers. The rest of the hexons seemed to be approximately ring-shaped with a roundish hole at their centers. Direct examination of electron micrographs and their optical diffraction patterns as well as Markham's rotational integration technique permitted the establishment of the mutual orientation of hexons and of polypeptide subunits within small, distinct parts of the crystalline array. The position of the hexons is such that one of the polypeptide subunits of a given hexon is situated nearest to the two other polypeptides of the neighboring hexon ('one-to-two' linkage system).