Telomeric Repeats - Non-identical telomeric repeats.... (Dec/06/2005 )
I have been delving into why telomeric repeats in chromosome ends would not be composed of identical units.
For an arbitrary example, instead of (GGGTTGG)^n (repeated n times), one may see:
(GGGTTGG)^n followed by (GGCTTGG)^m in the same chromosome end.
Could there possibly be two telomerases at work in the same system which could cause this? Any additional ideas would be most appreciated.
Which organism you are talking about? In humans I believe its (TTAGGG)n.
I also believed the repeats to be static in sequence. I will admit it has been a few years since I acively looked up telomere papers though.
I am pondering this generally, so the example in the initial question is organism aspecific.
Is the possibility of perhaps having two telomerases, with different affinities and RNA templates inherent to them? That could possibly create the above combination in the same telomere end? Any ideas or theories would be appreciated.
If we are allowed to make wild theories, here would be mine. Either, the organism is heterozygous for each "version of telomerase", thus resulting in different sequences, or telomerase does not have 100% fidelity in replicating the sequence from the RNA remplate it uses, since it is technically a reverse transcriptase. But that is just a wild speculation.
Yes, wild theories are *more* than welcome.
Regarding the fidelity theory, how might it "lose" fidelity ?
hi
i'm not sure to presence of different telomerase. As the RNA compound of the telomerase is encoded by many transcription islands, possibility of different polymerases implies a deregulation at some times. But in wild theory, assuming there is pssibility of non canonical appariements, only the first step of telomere elongation is critical. After first step, it's just like "photocopy". So why not?...
On the contrary, as many islands encode RNA, and as it's a critical step in cell surviving, i think a mechanism of protecion may degrade RNA that don't appariate on all bases. It's i think same processes as proof reading. And we are please to know that reparations are well done...
Regarding the fidelity theory, how might it "lose" fidelity ?
Like I said, wild speculation...as far as I know, and if anyone knows otherwise please let me know, reverse transcriptases do not have as high a fidelity rate as regular DNA or RNA polymerases. Thus, since it is a reverse transcriptase, perhaps it would follow that it would likewise have low fidelity...of course just wild speculation. There are of course significant differences between the way telomerase and viral RTs work.
Fidelity should not be very concerning here for telomerase. It just adds few hundred bases to the telomeric ends generally which are hexamer repeats.