Generation of Covalently Closed Circular DNA of Hepatitis B Viruses via Intracellular Recycling Is Regulated in a Virus Specific Manner

Persistence of hepatitis B virus (HBV) infection requires covalently closed circular (ccc)DNA formation and amplification, which can occur via intracellular recycling of the viral polymerase-linked relaxed circular (rc) DNA genomes present in virions. Here we reveal a fundamental difference between HBV and the related duck hepatitis B virus (DHBV) in the recycling mechanism. Direct comparison of HBV and DHBV cccDNA amplification in cross-species transfection experiments showed that, in the same human cell background, DHBV but not HBV rcDNA converts efficiently into cccDNA. By characterizing the distinct forms of HBV and DHBV rcDNA accumulating in the cells we find that nuclear import, complete versus partial release from the capsid and complete versus partial removal of the covalently bound polymerase contribute to limiting HBV cccDNA formation; particularly, we identify genome region-selectively opened nuclear capsids as a putative novel HBV uncoating intermediate. However, the presence in the nucleus of around 40% of completely uncoated rcDNA that lacks most if not all of the covalently bound protein strongly suggests a major block further downstream that operates in the HBV but not DHBV recycling pathway. In summary, our results uncover an unexpected contribution of the virus to cccDNA formation that might help to better understand the persistence of HBV infection. Moreover, efficient DHBV cccDNA formation in human hepatoma cells should greatly facilitate experimental identification, and possibly inhibition, of the human cell factors involved in the process

Changing profile of HIV-1 serotypes in Iceland during 1989-96

To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldA total of 63 HIV-1 strains collected in Iceland during the years 1989-96 were typed into serotypes A-E using a peptide-based enzyme immunoassay. The majority of the strains were of serotype B (66.6%). 22.2% were untypeable by this method. Until 1993 only serotype B was found, but in 1993 and after that date other serotypes, especially E (7.9%) were detected, indicating the spread of serotypes previously confined to developing countries. This may reflect the increase in the number of Icelanders travelling to distant countries and the increased immigration into Iceland from developing countries