In the last segment of ‘Intro to ERVs’, I explained part of my blags tagline by talking about gag, the gene that codes for all the retroviral structural proteins. This post is going to be about the gene(s) that code for all of the enzymes a retrovirus needs: pol.
But remember how I said retroviruses only have one promoter for alllll their genes? Sometimes retroviruses dont just have a pol gene, but gag-pro-pol, or gag-pro + pol, or something silly– lets just keep things simple and call it ‘pol‘ ?
Pol codes for all the enzymes a retrovirus needs:
- Protease– Chomps big proteins into all the little functional proteins, like we saw with Gag getting chomped into Matrix/Capsid/Nucleocapsid. The name ‘protease’ can be a little confusing because all organisms have ‘proteases‘, but only the protease that the retrovirus carries with it is the ‘right‘ protease to cleave in all the ‘right’ spots to get all the ‘right’ proteins in the end. Instead of giving retroviral proteases a special name, they just named it ‘Protease’. heh. Protease inhibitors are a great target for anti-retrovirals.
- Reverse Transcriptase– Another target for anti-retrovirals. Though the process of reverse transcription can be found in you and I (coooool), retroviruses need to carry an enzyme with them to convert viral RNA into DNA on demand. This process not only requires converting an RNA genome into a DNA genome, but also:
- RNase H– The RT enzyme has (at least) two active sites. One performs the process of reverse transcription. Another active site has RNase activity (chops up RNA, specifically, RNA Hybridized with DNA haha!). RNase H chews up the old RNA template after a single strand of DNA has been made, so the single strand of DNA can be made into double stranded DNA, and subsequently inserted into the host cells genome.
This might make more sense if you see this animation. *might* The process of reverse transcription is rather absurd.
- Integrase– Host cells dont come packed with the necessary biochemical machinery to move DNA out of the cytoplasm into the nucleus, to be inserted into the host DNA. So once again, retroviruses need to bring an enzyme capable of performing those activities. Integrase should be a perfect target for antiretrovirals… But we havent figured any out yet…
Okay, so weve got all the structural proteins. Weve got all the enzymatic proteins. What else does a retrovirus need?