Any microbiologists? DNA question

[Jon_in_london]

But I was under the impression that it was the CD4 cells that you lost when infected. And that once their count went below a certain amount the immune system was no longer able to protect you against other diseases. If HIV doesn't want to kill it's home why is it principly the cd4 counts that are looked at in patients and reduced? This seems counter intuitive to what I've previously read.

The CD4 counts will decrease but this is due to "collateral damage" rather than direct.

I guess the reason the CD4 count is still used is because it was developed by the medical community before the m.o. was properly known. It also probably gives a good indication as to the state of the immune system once AIDS has set in.

 

[svero]

Well this nef protiene is news to me! I had always assumed it was the infected cells that were dying. I was totally in the dark on that one.

With regards to an earlier question & answer - While reading up on Nef I came across an article that claims that hiv infected cells do in fact stop dividing.

http://www.sciencedaily.com/releases/2002/03/020304081315.htm

"At the center of it is the HIV protein Vpr, which stops infected T cells from dividing. In doing so, Vpr helps HIV to harness the infected cell’s resources to create more HIV."

 

[Jon_in_london]

Well this nef protiene is news to me! I had always assumed it was the infected cells that were dying. I was totally in the dark on that one.

With regards to an earlier question & answer - While reading up on Nef I came across an article that claims that hiv infected cells do in fact stop dividing.

http://www.sciencedaily.com/releases/2002/03/020304081315.htm

"At the center of it is the HIV protein Vpr, which stops infected T cells from dividing. In doing so, Vpr helps HIV to harness the infected cell’s resources to create more HIV."

Truth be told, Svero- my expertise in this matter begins to fail me at this point. I cant really speak with authority in this matter in any more depth. Please do continue research into it but beware the perils of the website. Much of what you will read is very old/simplistic/plain old nutty.

But enjoy!

 

[Shane Costello]

Originally posted by Jon_in_london:
Im sorry Shane but Bacterial genes most certainly DO have promoters (LacZ?)! However, a prokaryotic promoter wont necesarily work in a eukaryote. Indeed, promoter activity levels vary greatly even between one higher plant and another.

Isn't LacZ regulated by variable lactose concentration rather than DNA polymerase? Or am I wrong in presuming that a promoter sequence can only be acted upon by DNA polymerase?

 

[svero]

Truth be told, Svero- my expertise in this matter begins to fail me at this point. I cant really speak with authority in this matter in any more depth. Please do continue research into it but beware the perils of the website. Much of what you will read is very old/simplistic/plain old nutty.

But enjoy!

Sure...well this is just a small part of learning biology... a goal I set out for myself several months ago. The DNA book was actually not really meant to be part of that learning process. I picked it up purely for enjoyment. I have been slugging my way through ugrad textbooks on biology and microbiology but I wasn't far enough along to answer the questions brought up in the DNA book, and figured if I went to the textbooks for answers I might not be able to get plain language.

 

[Capsid]

Isn't LacZ regulated by variable lactose concentration rather than DNA polymerase? Or am I wrong in presuming that a promoter sequence can only be acted upon by DNA polymerase?

Yes that is right but the lactose switches on a regulator gene which then codes for a repressor protein which then binds to the operator region which then blocks binding of the RNA polymerase to the promoter site to stop mRNA synthesis. See this nice animation

Isn't nature wonderful?

 

[Capsid]

Hmm strange. I would have expected that the extra bits had to be paired off to fit into the structure nicely

I have just gone back to this and think you have misunderstood. When you say that the extra bits have to fit into the structure nicely, are you referring to the virus structure? If so this is not what I meant and not what happens. The viral DNA integrates into the host cell DNA and then the host cell divides (no virus particles need to exist). The provirus DNA, not the particle, is passed to the daughter cell as DNA not virus particle. Viruses don't have paired chromosmes, just DNA or RNA which may be single or double stranded.

One ploy could be to use nef deleted HIV as an attenuated vaccine candidate, unfortunatley pathogenesis and CD4 decline can still happen.

Death of uninfected cells is observed around infected cells and some work has shown that the secreted envelope of HIV can interact with CD4 and co-recpetors to initiate apoptosis (cell death ) events.

 

[Jon_in_london]

Isn't LacZ regulated by variable lactose concentration rather than DNA polymerase? Or am I wrong in presuming that a promoter sequence can only be acted upon by DNA polymerase?

RNA poymerase

 

[Shane Costello]

Originally posted by Jon_in_london:
RNA poymerase

That one was a typo, honest! Alarmed at my previous elementary blunder I returned to my molecular genetics notes from college. Bacterial (in general) genes lack introns. I knew that bacterial genomes were (usually) missing something.

Originally posted by Capsid:
Yes that is right but the lactose switches on a regulator gene which then codes for a repressor protein which then binds to the operator region which then blocks binding of the RNA polymerase to the promoter site to stop mRNA synthesis. See this nice animation

Isn't nature wonderful?

Merci Jacob et Monod. Nature is wonderful, but bacteria in particular are fascinating, given the whole range of environments they inhabit. My favourite is Thermophilus aquaticus, although I'm personally glad I'll never have to do another PCR again.