This family consists of the photosystem I reaction centre subunit IX or PsaJ from various organisms including Synechocystis sp. (strain pcc 6803), Pinus thunbergii (green pine) and Zea mays (maize). PsaJ Swiss:P19443 is a small 4.4kDa, chloroplastal encoded, hydrophobic subunit of the photosystem I reaction complex its function is not yet fully understood [1]. PsaJ can be cross-linked to PsaF Swiss:P12356 and has a single predicted transmembrane domain it has a proposed role in maintaining PsaF in the correct orientation to allow for fast electron transfer from soluble donor proteins to P700+ [1].

1: A large fraction of PsaF is nonfunctional in photosystem I complexes lacking the PsaJ subunit. Fischer N, Boudreau E, Hippler M, Drepper F, Haehnel W, Rochaix JD; Biochemistry 1999;38:5546-5552. PMID:10220342

2: Genes encoding eleven subunits of photosystem I from the thermophilic cyanobacterium Synechococcus sp. Muhlenhoff U, Haehnel W, Witt H, Herrmann RG; Gene 1993;127:71-78. PMID:8486290