CELLULAR PROTEINS THAT BIND TO THE HEPATITIS-B VIRUS POSTTRANSCRIPTIONAL REGULATORY ELEMENT

The hepatitis B virus posttranscriptional regulatory element (PRE), wh ich resides in the 3' region of the viral S transcripts, is important for the high-level expression of these mRNA species. We have previousl y shown that the PRE acts intranuclearly in cis to allow efficient exp ort of intronless transcripts into the cytoplasm, in a manner that is independent of viral transacting factors. We here present data demonst rating that there are widely dispersed subelements in the PRE that are important for its function. All of these subelements bind, albeit wit h different affinities, to the same or similar host nuclear factor(s) containing two proteins, approximately 30 and 45 kDa in mass. The affi nity of protein binding to a subelement is positively correlated with the ability of the subelement to activate intronless gene expression. Therefore, it appears that the PRE functions by having multiple bindin g sites for nuclear proteins that may be directly or indirectly involv ed in export of unspliced mRNA species. (C) 1996 Academic Press, Inc.