This family contains several Photosystem I reaction centre subunit N (PSI-N) proteins. The protein has no known function although it is localised in the thylakoid lumen [1]. PSI-N is a small extrinsic subunit at the lumen side and is very likely involved in the docking of plastocyanin [2].

1: The interaction between plastocyanin and photosystem I is inefficient in transgenic Arabidopsis plants lacking the PSI-N subunit of photosystem I. Haldrup A, Naver H, Scheller HV; Plant J 1999;17:689-698. PMID:10230065

2: Pigment organization and energy transfer dynamics in isolated photosystem I (PSI) complexes from Arabidopsis thaliana depleted of the PSI-G, PSI-K, PSI-L, or PSI-N subunit. Ihalainen JA, Jensen PE, Haldrup A, van Stokkum IH, van Grondelle R, Scheller HV, Dekker JP; Biophys J. 2002;83:2190-2201. PMID:12324436