Involved in the regulation of glutamyl-tRNA reductase (GluTR) which is important for the synthesis and distribution of 5-aminolevulinate, a precursor in heme and chlorophyll biosynthesis (PubMed:22180625). Stimulates GluTR activity and regulates glutamate-1-semialdehyde release. May play a role in heme metabolism (PubMed:24753615). Necessary for efficient photosynthetic electron transport in chloroplasts (PubMed:20657737). Interacts with HEMA1 (PubMed:22180625, PubMed:24753615) and forms a heterotetramer of two GLUTRBP and two HEMA1 subunits (PubMed:24753615). Detected at low levels in thylakoids. Reduced growth, slightly pale green leaves, reduced levels of chlorophyll and heme, and low non-photochemical quenching (NPQ).