GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE SELECTIVELY BINDS AU-RICH RNA IN THE NAD(-BINDING REGION (ROSSMANN FOLD)())

A 36-kDa protein that binds AU-rich RNA was purified from human spleen and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). C ARER has been previously demonstrated to bind tRNA with high affinity. Competition studies suggested that cytoplasmic GAPDH binds the AU-ric h elements (AREs) of lymphokine mRNA 3'-untranslated regions with high er affinity than tRNA. The AUUUA-specific RNA binding activity of GAPD H was inhibited by NAD(+), NADH, and ATP in a concentration-dependent manner, suggesting that RNA binding of GAPDH might involve the NAD(+)- binding region, or dinucleotide-binding (Rossmann) fold. This hypothes is was supported by experiments that localized RNA binding to the pred icted N-terminal 6.8-kDa peptide, known to be involved in the formatio n of the NAD(+)-binding domain. The direct demonstration of ARE-specif ic binding protein activity localized to the NAD(+)-binding region of GAPDH supports the general concept that enzymes containing this domain may exhibit specific RNA binding activity and play additional roles i n nucleic acid metabolism. Finally, cytoplasmic GAPER was found in the polysomal fraction of T lymphocytes. Thus, the RNA binding specificit y of GAPDH as well as its localization within the cell merit its stron g consideration as a protein important in the regulation of ARE-depend ent mRNA turnover and translation in addition to its well described ro le in glycolysis.