This is the N-terminal domain of proteins from photosynthetic organisms including plants and cyanobacteria, such as Tab2 proteins. Tab2 was first identified in Chlamydomonas reinhardtii as a RNA binding protein required for translation of the chloroplast PsaB photosystem I subunit [1]. Later, the Tab2 homologue (ATAB2) from Arabidopsis was found involved in the signalling pathway of light-controlled synthesis of photosystem proteins during early plant development [2], presumably functioning as an activator of translation with targets at PSI and PSII [3].

1: Tab2 is a novel conserved RNA binding protein required for translation of the chloroplast psaB mRNA. Dauvillee D, Stampacchia O, Girard-Bascou J, Rochaix JD; EMBO J. 2003;22:6378-6388. PMID:14633996

2: ATAB2 is a novel factor in the signalling pathway of light-controlled synthesis of photosystem proteins. Barneche F, Winter V, Crevecoeur M, Rochaix JD; EMBO J. 2006;25:5907-5918. PMID:17139246

3: Large-scale genetic analysis of chloroplast biogenesis in maize. Belcher S, Williams-Carrier R, Stiffler N, Barkan A; Biochim Biophys Acta. 2015;1847:1004-1016. PMID:25725436