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cccDNA (covalently closed circular DNA) is a special DNA structure that arises during the propagation of some viruses in the cell nucleus and may remain permanently there. It is a double-stranded DNA that originates in a linear form that is ligated by means of DNA ligase to a covalently closed ring.
This cccDNA serves as a template for transcription of four viral mRNAs by host RNA polymerase. The largest mRNA, (which is longer than the viral genome), is used to make the new copies of the genome and to make the capsid core protein and the viral DNA polymerase .
HBeAg is an antigen that can be found between the icosahedral nucleocapsid core and the lipid envelope (the outer most layer of the hepatitis b virus).However, HBeAg is considered "nonparticulate" or "secretory". [2]
A covalently closed, circular DNA (also known as cccDNA) is topologically constrained as the number of times the chains coiled around one other cannot change. This cccDNA can be supercoiled, which is the tertiary structure of DNA. Supercoiling is characterized by the linking number, twist and writhe.
Circular DNA is DNA that forms a closed loop and has no ends. Examples include: Plasmids, mobile genetic elements; cccDNA, formed by some viruses inside cell nuclei; Circular bacterial chromosomes
The structure of hepatitis B virus. Hepatitis B virus is a member of the Hepadnavirus family. [11] The virus particle, called Dane particle [12] (), consists of an outer lipid envelope and an icosahedral nucleocapsid core composed of protein.
The cccDNA is then transcribed to RNA via host cell RNA polymerase. [8] Many RNAs are shipped to the cytoplasm where the proteins are assembled, including a large number of empty capsids. Reverse transcription by the viral polymerase protein re-creates the relaxed, partially double-stranded circular DNA genome.
This is then translocated to the nucleus, where the partially double stranded DNA is 'repaired' by the viral polymerase to form a complete circular dsDNA genome (called covalently-closed-circular DNA or cccDNA). The genome then undergoes transcription by the host cell RNA polymerase and the pregenomicRNA (pgRNA) is sent out of the nucleus. The ...