Figure 1.

In Situ Architecture of Septal Junctions Reveals Tube, Plug, and Cap Modules

(A and B) Cryotomograms (magnified views in boxes) of a FIB-milled Anabaena filament. The two different slices at different Z-heights show the septum between adjacent vegetative cells. Multiple SJs were seen crossing the septum (arrowheads). The SJ lengths were precisely adjusted to the septum thickness. CM, cytoplasmic membrane; OM, outer membrane; PB, phycobilisomes; PG, septal peptidoglycan; TM, thylakoid membranes. Bars, 100 nm. Shown are projections of 13.5 nm-thick slices.

(C–F) Subtomogram averaging of SJ ends revealed three structural modules: tube, cap, and plug. Shown is a 0.68 nm-thick tomographic slice through the average (C), a schematic representation of SJ modules (D; modules segmented in different shades of green), and oblique (E) and top (F) views of a surface representation (modules were segmented to match colors in D). The cap consisted of a ceiling that was held by five arches. Bars, 10 nm.

See also Figures S1 and S2 and Videos S1 and S2.