Figure 3 Electron micrographs and processed top
views of the-PSI trimer and CP43-PS1 supercomplex. Shown are
typical electron micrographs of-PSI trimers (a) and CP43'-PSI
complex (b) in negative stain; scale bar, 50 nm. Most complexes
are top views, probably of the stromal surface (ringed), but
occasional side views were observed (boxed). Also shown are
image-processed top views of negatively stained-PSI trimers
(c) and CP43'--PSI complexes (d). The projection maps were obtained
by averaging 4,000-PSI trimer and 3,000 CP43'-PSI particles.
Note that the iron-stress-induced complex contains a trimer
of-PSI surrounded by a 55 Angstrom-thick ring of density corresponding
to 18 copies of CP43'. The-PSI trimer in (c) is surrounded by
a detergent layer that accounts for its slightly larger size
compared with the trimer within the CP43'-PSI complex. Similarly,
the 55 Angstrom ring of the latter complex also contains an
outer detergent shell.
