IDENTIFICATION OF GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE AS A CELLULAR PROTEIN THAT BINDS TO THE HEPATITIS-B VIRUS POSTTRANSCRIPTIONAL REGULATORY ELEMENT

The hepatitis B virus posttranscriptional regulatory element (PRE) is an RNA cis-element that is required for high-level expression of viral surface gene transcripts and appears to function by activating mRNA e xport to the cytoplasm. We have previously shown that multiple fragmen ts of the PRE bind to two cellular proteins of approximately 35 and 55 kDa in molecular mass and that this binding correlates with function. By a combination of column chromatographic techniques and SDS-polyacr ylamide gel electrophoresis, we have been able to purify the smaller p rotein. Amino-terminal sequencing of the purified protein shows identi ty to glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an RNA-binding glycolytic enzyme that has been implicated in the export of tRNA. Imm unoprecipitation analysis reveals that GAPDH is indeed present in the protein-RNA complex resulting from incubation of crude nuclear extract s with a functional region of the PRE. Furthermore, binding of the cel lular 35 kDa protein to the PRE fragment is blocked by NAPDH, as would be expected for RNA binding by GAPDH. Finally purified commercial GAP DH also binds specifically to this RNA fragment. Therefore, GAPDH is o ne of the cellular proteins that binds to the PRE, and may be involved in the posttranscriptional regulation of hepatitis B virus gene expre ssion. (C) 1998 Academic Press.