1.V.1.1.1
Cyanobacterial septa (also called microplasmodesmata) between vegetative cells and between vegetative cells and N₂-fixing heterocysts that appear to include at least 3 proteins:  SepJ, which is a member of the DMT superfamily (2.A.7.3.81) and seems to transport acidic amino acids and other hydrophilic amino acids, as well as FraC, and FraD which seem to be cyanobacterium-specific (Nürnberg et al. 2015). FraC and FraD each have 4 or 5 and 5 TMSs, respectively, and are encoded in a single operon, fraCDE. The septa have a mean diameter of about 7 - 8 nm with varying numbers of nanopores (holes in the peptidoglycan) (Flores et al. 2018). Each septa has a cap and a cyanophycin plug as well as a cytoplasmic membrane-anchored tube crossing the intercellular space between cells. The AmiC amidase may drill holes in the peptidoglycan druing septal biogenesis to generate the nanopores. The septa can transport a variety of sugars, amino acids, peptides and 5-carboxyflorescein. Proteins that affect nanopore formation include the product of the alr3353 gene (SjcF1; 760 aas; a peptidoglycan binding protein LytM-like factor) which is homologous to B. subtilis proteins in gap junction-like structures (TC# 1.A.34.1.1-3) and the SpoIIA-SpoQ2 complex (TC# 9.B.70.1.1) (Flores et al. 2018).