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Old 06-26-2011
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Virus Hepatitis B Reverse Transcriptase?

from what I understand....


Hepatitis B has reverse transcriptase.... meaning "RNA DEPENDENT DNA POLYMERASE"

but in the FIRST AID it says

For HEP B-

"REVERSE TRANSCRIPTASE, TRANSCRIBES DNA GENOME FROM RNA INTERMEDIATE. HOWEVER, THE VIRION ENZYME IS A DNA DEPENDENT DNA POLYMERASE"


can someone please explain this concept?:sorry:
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Old 06-27-2011
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So there is a little more complexity to the picture than is made apparent by First Aid (as always).

So as it says, the packaged enzyme is actually a DNA dependant DNA polymerase. However, HBV does indeed need a reverse transcriptase.

So as you remember, HBV has a PARTIALLY DsDNA. Meaning that part of its genome is single stranded and part is double stranded. It is however still circular.

There is a + and - sense strand of the DNA and the partial strand is + sense and the - strand makes a full circle. So hopefully that gives a visual of what the genome looks like. So as we know, HBV likes to replicate inside of the nucleus. Once this genome gets into the nucleus, it uses its packaged DNA dependant DNA polymerase to fill in the rest of the DNA to make it into a FULLY dsDNA. So basically it uses the - strand as a template to fill in the rest of the + strand. The DNA is then processed in multiple ways and makes what is called cccDNA. It stands for i think (look this part up) covalent closed circular DNA. The - strand serves as the template for the viral mRNA. So the - strand of the cccDNA is read by HOST cell RNA-polymerases and viral mRNA are made.

There are 4 mRNA product, and one of them is is actually longer than the entire viral genome. This mRNA is what is used for making more viral DNA for packaging into the virions.

These viral mRNA travel out to the nucleus and code for all the proteins required for viral proliferation and or whatever else. One of the gene products is a REVERSE TRANSCRIPTASE. The mRNA molecules undergo further modification in the cytoplasm to extend their life. At this point, the "long mRNA" segment will travel back into the nucleus and be processed by the reverse transcriptase to make copies of the circular, partially dsDNA of HBV. So thats why even though there is a reverse transcriptase, the packaged (virion) enzyme is a DNA-dep-DNA polymerase.

*IN SHORT*

DNA dependent DNA polymerase: needed for post entry modification of viral genome in the nucleus (therefore MUST be packaged into viron)

RNA dependent DNA polymerase: needed for producing viron dsDNA from mRNA transcript (therefore not packaged into virion)

Hope this helps! Let me know if there are any mistakes!

Last edited by spaidak2; 06-27-2011 at 07:27 AM. Reason: uhhhhhh
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Old 07-14-2012
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Quote:
Originally Posted by spaidak2 View Post

RNA dependent DNA polymerase: needed for producing viron dsDNA from mRNA transcript (therefore not packaged into virion)

Hope this helps! Let me know if there are any mistakes!
so why RNA dependent DNA polymerase is not need to be packed in the virion? how can virus produce more its genome without this enzyme?
Thanks
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