Arrangement of morphological subunits in bacterial spinae.

The filament, that is helically arranged to form the bacterial spina, is composed of morphological subunits (oligomers) about 5.6 nm in width and 11 nm in length. The oligomers are asymmetrical in that the inner surface is grooved. Image analysis of negative-stained spinae ribbons indicates that the oligomers are paired, possibly beaded structures, the arrangement of which is easily distorted during preparation. In intact spinae, the oligomer orientation may be normal to the filament axis, but in collapsed freeze-etched spinae, the oligomers are inclined at a constant angle of about 72 degrees to the filament axis.