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polyadenylation signal - What is it? (Mar/20/2006 )

Hi everyone,

I am trying to understand some of the characteristics of plasmids:

- What is it a polyadenylation signal? Eg. BGH polyA or SV40 polyA?

- Can you give me eg. of procaryotic and eucaryotic promoters? High and Low copy number?



basically, we should return to the basics of a gene.
A gene is a promoter, a coding seq and a termination sequence.
Regarding pol III promoters, transcription termination occurs after TTTT
Regarding pol II-U1 promoter, transcription occurs in the 3' box, a well known sequence.

Regarding general pol II-"mRNA-giving" genes, transcription termination is little more confuse. you have at the end of the DNA sequence a "polyadenylation" sequence (consensus one is AATAAA on DNA, AAUAAA on mRNA) and the termination of transcription is 20 - 50 bp after it. But does it play a role in transcription termination? nothing is very clear at time

This sequence is also found in the mature mRNA transcript, and recruits the Poly A polymerase, which add several A to the end of mRNA. Then this sequence (the poly A tail) is bound by poly A binding protein, which recruits others proteins, and the complex goes to connect by non covalent bonds the 7Me-guanosine cap. Toghether, these partenaries ensure the stability of the mRNA transcript.

Regarding stability, a mRNA lacking poly A tail does not survive more than 5-10' (if my memory doesn't fail biggrin.gif) but the destruction process may be shorter.

So to sum up, the polyadenylation signal is added to the end of an insert, to ensure the polyadenylation of the mRNA, and a to participate to correct termination of transcription, in same instance. As SV40polyA signal is very well known and as the SV40 PA signal play a role in terminationof transcription, it's the one routinely used.

So i hope ths reply gives you the needed infos.