The Lysogenic cycle in viruses

[yestomeds]

Hi all,

There's 2 types of cycles: lytic and lysogenic.
A) About the lysogenic cycle, is it the case that when the viral genome is sitting tight when within the host genome, BUT that it does make (translate + transcribe a protein product) a certain protein even whilst "dormant"/not doing anything, called a repressor protein?

B) This repressor protein then just sits by the viral genome to prevent activity, right?

C) Also, I wrote down in my old notes that transcription factors, in addition to repressor proteins... anybody know why I would have done that haha?

D) If, and when, this lysogenic type of a virus is ready to leave, it excises itself - is this when it becomes just like the lytic cycle, i.e. in its coming out of the host, kind of lyses/kills host membrane?

Thank you! 🙂

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[Axes]

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[yestomeds]

What? @Axes

 

[shefv]

Someone correct me if I am wrong.

Yes, the repressor genes make sure the viral genome is not transcribed and translated. The transcription factors are inactive since we don't want transcription to occur. When the virus leaves the lysogenic life cycle, it enters the lytic life cycle but I think it can also enter the productive life cycle where the new viral particles leave via budding if this was an animal host cell.

 

[basophilic]

For A, yeah it probably needs to make repressor protein if it wants to stay as a provirus for a while; however, I'd expect the protein to be translated (and transcribed if DNA-based or -RNA virus) entirely in the cytoplasm. My speculation but I wouldn't expect the integrated viral genome to be transcribed since the virus wouldn't want transcript to interact with the various processing machinery. It'd be much easier practically to do it in the cytoplasm.
For D, shefv is right; it will leave via lytic cycle if in a bacterium or via budding if in an animal cell - however, budding doesn't usually kill the host cell; the virus just takes a scoop of cytoplasm and part of the membrane; the host cell would still stay alive.

 

[yestomeds]

Thanks so much you two. D totally makes sense now. So A would def need to happen immediately so that, upon (after) incorporation into genome, repressor proteins are ready to go. <-- is this correct?
(Oh side note and yes, unless you're +ran, then no transcription needed).

Can you still explain C? Thank you 🙂