The hook and basal body are quite different from the filament
(figure 3.42). Slightly wider than the filament, the hook is made of
different protein subunits. The basal body is the most complex
part of a flagellum. In the earliest-made transmission electron
micrographs of the basal bodies of E.coli and most other gramnegative
bacteria, the basal body appeared to have four rings—L ring, P ring, S ring, and M ring—connected to a central rod
It is now known that the S ring and M ring are different
portions of the same protein, and they are now referred to
as the MS ring. A later discovery was the C ring, which is on the
cytoplasmic side of the MS ring. Gram-positive bacteria have
only two rings—an inner ring connected to the plasma membrane
and an outer one probably attached to the peptidoglycan