The arginine-rich domain of hepatitis B virus precore and core proteins contains a signal for nuclear transport

Precore and core proteins are two co-carboxy-terminal proteins of B virus. Precore protein contains the entire sequence of core protein plus an amino-terminal extension of 29 amino acid residues. Both proteins can display a common antigenic determinant as core antigen (HBcAg). Clinically, HBcAG is detected in the nucleus, cytoplasm, or of hepatitis B virus-infected hepatocytes. In order to understand the mechanism that regulates nuclear transport of HBcAg, various portions of precore and core proteins were linked to a reporter protein, human alpha-globin, andexpressed in mammalian cells. Our results indicate that the precore protein-specific sequence, although important for nuclear transport, does not contain a nuclear localization singnal. Instead, a singal for nuclear transport is located near the carboxy termini of Precore and core proteins in the arginine-rich domain. This signal is made up of a set of two direct PRRRRSQS repeats and is highly conserved among mammalian hepadnaviruses.