Identification of bovine glutamate dehydrogenase as an RNA-binding protein

Two RNA binding activities were demonstrated in bovine liver homogenate. One binding protein was isolated by a simple ion exchange and gel filtration protocol and was shown by N-terminal protein sequence analysis to be glutamate dehydrogenase. Using identical RNA substrate and assay conditions, no detectable RNA binding was observed with equimolar amounts of other representative dehydrogenases and proteins. Furthermore, excesses of tRNA, salmon testis DNA, or each of the four homoribopolymers were unable to compete for the RNA-binding site. Total cytosolic RNA, however, successfully prevented binding of radiolabeled RNA substrate. These data are consistent with glutamate dehydrogenase containing a binding site for heteropolymeric RNA with highest affinity for an as yet undefined nucleotide consensus sequence or structure. The potential physiological relevance of these observations is discussed.