Structures of PSI oligomers from cyanobacteria. (A) PSI core monomer from Thermosynechococcus elongatus (6LU1). (B) Cyanobacterial PSI core trimer (7COY). (C) PSI core tetramer from Anabaena sp. PCC 7120 (6JEO). (D) PSI-IsiA supercomplex from Synechococcus elongatus PCC 7942 (6KIF). (E) Superposition of PsaL from the PSI core monomer in Thermosynechococcus elongatus (6LU1), the PSI core trimer (7COY), the PSI core tetramer in Anabaena sp. PCC 7120 (6JEO), and the PSI-IsiA supercomplex Synechococcus elongatus PCC 7942 (6KIF). (F) Sequence alignment of the PsaL protein from the PSI core monomer, PSI core trimer, PSI core tetramer, and PSI-IsiA supercomplex. The abbreviations used are as follows: A. m.: Acaryochloris marina (cyanobacteria), S. e.: Synechococcus elongatus PCC 7942 (cyanobacteria), T. e.: Thermosynechococcus elongatus (cyanobacteria), A. sp.: Anabaena sp. PCC 7120 (cyanobacteria). Color codes used are as follows (except PsaA and PsaB in panels (A–D) that are not labeled): PsaF, red; PsaI, green; PsaJ, cyan; PsaK, light-blue; PsaL, magenta; PsaM, yellow; PsaE, blue; PsaD, wheat; PsaP, split-pea. Color codes of PsaL in panel (E): PsaL from Thermosynechococcus elongatus (red); PsaL from Acaryochloris marina (yellow); PsaL from Anabaena sp. PCC 7120 (magenta); PsaL from Synechococcus elongatus PCC 7942 (green).