Hepatitis B virus (HBV), the causative agent of chronic hepatitis B and prototypic hepadnavirus, is a small DNA virus that replicates by protein-primed reverse transcription. The product is a 3-kb relaxed circular DNA (RC-DNA) in which one strand is linked to the viral polymerase (P protein) through a tyrosyl-DNA phosphodiester bond. Upon infection, the incoming RC-DNA is converted into covalently closed circular (ccc) DNA, which serves as a viral persistence reservoir that is refractory to current anti-HBV treatments. The mechanism of cccDNA formation is unknown, but the release of P protein is one mandatory step. Structural similarities between RC-DNA and cellular topoisomerase-DNA adducts and their known repair by tyrosyl-DNA-phosphodiesterase (TDP) 1 or TDP2 suggested that HBV may usurp these enzymes for its own purpose. Here we demonstrate that human and chicken TDP2, but only the yeast ortholog of TDP1, can specifically cleave the Tyr-DNA bond in virus-adapted model substrates and release P protein from authentic HBV and duck HBV (DHBV) RC-DNA in vitro, without prior proteolysis of the large P proteins. Consistent with TPD2's having a physiological role in cccDNA formation, RNAi-mediated TDP2 depletion in human cells significantly slowed the conversion of RC-DNA to cccDNA. Ectopic TDP2 expression in the same cells restored faster conversion kinetics. These data strongly suggest that TDP2 is a first, although likely not the only, host DNA-repair factor involved in HBV cccDNA biogenesis. In addition to establishing a functional link between hepadnaviruses and DNA repair, our results open new prospects for directly targeting HBV persistence.hepatitis B virus persistence | TDP substrate specificity | virus-DNA repair interface M ore than 250 million people worldwide are chronically infected with hepatitis B virus (HBV) (1) and are at a highly increased risk for developing end-stage liver disease (2). Current treatments with IFN-α or nucleos(t)ide analogs (NAs) are only partially effective (3, 4). Importantly, they do not directly target the viral persistence reservoir, an episomal covalently closed circular (ccc) DNA form of the viral genome that serves as template for all viral transcripts; hence a few cccDNA molecules present in the liver can reactivate full viral replication. Eliminating infection thus will require the elimination of cccDNA. cccDNA is generated, upon infection, from the viral polymerase (P protein)-linked relaxed circular (RC) DNA present in incoming virions (Fig. 1A). The mechanism by which RC-DNA is converted to cccDNA is poorly understood, but it must involve multiple steps (see below). Because the ∼3-kb genomes of HBV and the other hepadnaviruses [e.g., from ducks (DHBV)] are too small to encode all the activities required for this conversion, these activities must be provided by the host cell.RC-DNA from all hepadnaviruses bears several molecular peculiarities that result from its generation by protein-primed reverse transcription (for reviews, see refs. 5 and 6). The pregenomic RNA (p...

A biochemical concept is proposed for a radioiodinated fatty acid avoiding high iodine background in imaging studies of the myocardium. For this approach omega-(p-123I phenyl)-pentadecanoic acid is chosen and a method for synthesis and quality control described.

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