Cytosolic folylpolyglutamate synthase catalyzes the reaction of 5-methylTHF-glutamate(n), L-glutamate, and ATP to form 5-methylTHF-glutamate(n+1), ADP, and orthophosphate. (The first glutamate residue is attached to the glutamate moiety of 5-methylTHF itself; for convenience the process is annotated here as if it proceeded in a single concerted step.) The extent of conjugation is variable, but the commonest cytosolic form of 5-methylTHF has five added glutamate residues. Although its properties as a donor of one-carbon units are not affected by glutamate addition, 5-methylTHF that lacks added glutamate residues cannot be retained in the cytosol so this reaction is needed for normal 5-methylTHF function under physiological conditions (Garrow et al. 1992; Chen et al. 1996).