The hepatitis B virus (HBV) contains DNA and polymerase in a viral capsid made by the core protein; this central region is surrounded by a lipid envelope that contains large, middle and small envelope proteins (top right; middle and small proteins not shown). In order to enter a liver cell, the virus binds to a receptor on the surface of the cell through the pre-S1 domain of the large envelope protein (L). Yan, Zhong and co-workers have now shown that a protein known as NTCP is a receptor for HBV. On entering the cell, the DNA inside the virus is transported to the nucleus, where it is converted to covalently closed circular DNA. This DNA serves as a template to produce subgenomic RNA, which encodes for the three envelope proteins: these proteins are synthesized in the endoplasmic reticulum (ER). It also produces pregenomic RNA, which encodes for the core protein and the polymerase, and the polymerase/pregenomic RNA complex is then packaged with the core protein to form the viral capsid (inside which the polymerase converts the pregenomic RNA into viral genomic DNA). This capsid then acquires a lipid envelope containing the viral envelope proteins, and the mature viruses are released from the cells.