Intrinsic DNA synthesis fidelity of XMRV reverse transcriptase

[Jemal]

Anyone know what this means?

Intrinsic DNA synthesis fidelity of xenotropic murine leukemia virus-related virus reverse transcriptase

Vernica Barrioluengo1, Yi Wang2, Stuart F. J. Le Grice2, Luis Menndez-Arias1,*

Abstract
Although recent reports have provided strong evidence to suggest that xenotropic murine leukemia virus-related virus (XMRV) is unlikely to be the causative agent of prostate cancer and chronic fatigue syndrome, this recombinant retrovirus can nonetheless infect human cells in vitro and induce a chronic infection in macaques. We have determined the accuracy of DNA synthesis of the reverse transcriptases (RTs) of XMRV and Moloney murine leukemia virus (MoMLV) using a combination of pre-steady-state kinetics of nucleotide incorporation and an M13mp2-based forward mutation assay. The obtained results have been compared with those previously reported for the human immunodeficiency virus type 1 BH10 strain (HIV-1BH10) RT. MoMLV and XMRV RTs were 13.9 and 110 times less efficient (as determined by kpol/Kd) than the HIV-1BH10 RT in incorporating correct nucleotides. Misinsertion and mispair extension kinetic studies demonstrated that MoMLV RT was more accurate than the HIV-1BH10 RT. In comparison with MoMLV RT, the XMRV enzyme showed decreased mispair extension fidelity and was less faithful when misincorporating C or A opposite A. However, the XMRV RT showed stronger selectivity against G in misinsertion fidelity assays. Forward mutation assays revealed that XMRV and MoMLV RTs had similar accuracy of DNA-dependent DNA synthesis, but were >13 times more faithful than the HIV-1BH10 enzyme. The mutational spectra of XMRV and MoMLV RTs were similar in having a relatively higher proportion of frameshifts and transversions, compared with the HIV-1BH10 RT. However, the XMRV polymerase was less prone to introduce large deletions and one-nucleotide insertions.

http://onlinelibrary.wiley.com/doi/10.1111/j.1742-4658.2012.08532.x/abstract

 

[Bob]

Anyone know what this means?

Good question Jemal!

On first reading, it seems to contradict itself.

I can't work out if XMRV RT has 13 times the mutation rate of HIV, or 13 times less!

I'll try reading again when i'm less tired!

 

[maddietod]

I read the thread title and wondered what all those words meant.

I laughed out loud when Jemal said "Anybody know what this means?"

Yeah, I get it that you meant what did the PAPER mean. But I had that savory moment of feeling less alone in my cluelessness.

Thanks.

 

[VillageLife]

I sure miss doctor mikovits, it's times like this she explained everything to us.

 

[Bob]

OK, I've looked at it again, and I'm not sure if I understand any of it or not...

Well, I thought I understood some of it, but from my uneducated perspective, it seems to contradict itself...

One bit seems to say that the replication accuracy of XMRV and MoMLV is 13 times more than HIV, and another bit seems to say that the replication accuracy of MoMLV & XMRV is 13.9 to 110 times less than HIV RT.


So, this is how I understand it...

They used two methods to compare the accuracy of the 'reverse transcriptase' enzyme (RT) (for DNA synthesis) of XMRV, MoMLV and a strain of HIV.

The inbuilt inaccuracy of reverse transcriptase (RT), in viruses, is one of the reasons why many viruses have a very high mutation rates.

So, this study is looking at the mutation rates of XMRV, MoMLV and HIV.


One method of measurement seems to give an accuracy for XMRV and MoMLV RT that is 13 times "more faithful" than HIV RT, and then another method seems to give an accuracy for MoMLV and XMRV RTs that were 13.9 and 110 times "less efficient" than HIV in incorporating correct nucleotides.

So, unless I've misunderstood it, which it highly likely, it seems to have conflicting/opposing results, depending on the method of measurement used.

Two different methods are used for the different results, but I don't understand why there would be such a high discrepancy between the two set of results...

Maybe the last couple of sentences might give the answer?:

"The mutational spectra of XMRV and MoMLV RTs were similar in having a relatively higher proportion of frameshifts and transversions, compared with the HIV-1BH10 RT. However, the XMRV polymerase was less prone to introduce large deletions and one-nucleotide insertions."

This quote seems to suggest that there are different types (patterns) of mutation, as follows...

XMRV shows less variation to the other two viruses in one type of mutation pattern (it is less prone to introduce large deletions and one-nucleotide insertions).
Whereas XMRV and MoMLV show more variation than HIV in the other type of mutation pattern (they have a relatively higher proportion of frameshifts and transversions).

I don't know how to interpret all of this...

It has been suggested in the past that XMRV might have a low mutation rate like HTLV... Does this study back that up?


Disclaimer: Well, that's my best shot, but it's quite possible that I've got all of this totally wrong!!!


And now I've given myself a headache!! :headache:

 

[Jemal]

Thanks for trying to interpret Bob!
I still think the title of this report is made out of random words thrown together.

 

[Bob]

Thanks for trying to interpret Bob!
I still think the title of this report is made out of random words thrown together.

lol, I think you're right Jemal...

So I've juggled the words around, and it seems to make just as much sense!!!

Reverse fidelity of Intrinsic XMRV DNA transcriptase synthesis