Biochemical characterization of the 94- and 78-kilodalton glucose-regulated proteins in hamster fibroblasts.

This report concerns further characterization of the 94-kDa and the 78-kDA glucose-regulated proteins which are the major proteins overproduced in hamster fibroblasts when the cells are starved of glucose. Using a temperature-sensitive mutant, K12, which synthesizes high levels of these proteins at the nonpermissive temperature, we purified both proteins by two-dimensional gel electrophoresis and determined their amino acid compositions as well as the NH2-terminal sequences. Both proteins contain an unusual NH2-terminal sequence rich in glutamic and aspartic acid residues. Biochemical fractionation of these proteins demonstrated that the 78-kDa glucose-regulated protein is present in the nuclear fraction. In addition, we show that phosphate incorporation into the 78-kDa protein is specifically affected in the K12 mutant cells.