Every known example of the phenylalanyl-tRNA synthetase, except the monomeric form of mitochondrial, is an alpha 2 beta 2 heterotetramer. The beta subunits break into two subfamilies that are considerably different in sequence, length, and pattern of gaps. This model represents the subfamily that includes the beta subunit from Bacteria other than spirochetes, as well as a chloroplast-encoded form from Porphyra purpurea. The chloroplast-derived sequence is considerably shorter at the amino end. [Protein synthesis, tRNA aminoacylation]
Jiyao W et al.(2023). "The conserved domain database in 2023.",