Identification of Translin/Trax complex as a glucose response element binding protein in liver.

Previously, we found a novel protein factor in the livers of rats fed a high-carbohydrate diet, which binds to the major late transcription factor (MLTF)-like site within the glucose response element (GRE) of the liver-type pyruvate kinase (L-PK) gene [J. Biol. Chem. 274 (1999) 1100]. This factor, termed glucose response element binding protein (GRBP), exists in both liver cytosol and nucleus. In order to identify GRBP, we purified to homogeneity cytosolic GRBP from rat liver extract and identified it as a Translin/Trax heteromeric complex. Based on partial amino acid sequences, we have cloned full-length rat cDNAs of both Translin and Trax. The nuclear and the cytosolic Translin/Trax complex were both large polymers of 240 and 420 kDa, respectively. The molar ratio of Translin/Trax in the polymers was 2:1 in the liver cytosols. The nuclear and cytosolic Translin/Trax complexes as well as expressed His-tagged Translin bound to double- and single-stranded MLTF sites of the GRE of L-PK gene more avidly than to single-stranded Bcl-CL1, which was initially thought to be specific for Translin. Our findings indicate that the Translin/Trax complex constitutes the previously described GRBP, and that this complex binds the GRE of the L-PK gene with high affinity. The precise physiologic role of GRBP, however, remains unclear.