SV40 poly(A) signal works bidirectionally?
kay at lyon151.inserm.fr
Wed Feb 5 11:27:51 EST 1997
In article <199702011239.VAA47036 at sutnfs.rs.noda.sut.ac.jp>,
ohba at rs.noda.sut.ac.jp says...
>Hello! I am using pREP4 and pREP9 vectors from Invitrogen. Looking at the
>vector sequences provided by the vendors, I found that the direction of
>SV40 poly(A) signal sequences of pREP vectors (405-6 of pREP4, 692-1090 of
>pREP9) are opposite to that of a pBK vector (750-469 of pBK-RSV) from
>Stratagene. All the signal sequences are placed downstream to multiple
>cloning sites. Does SV40 poly(A) signal work bidirectionally?
Not really. In SV40, the early genes are transcribed off of one strand and
the late genes off of the other. The two promoters are grouped near the
origin of replication at position 1. Similarly, the two distinct
polyadenylation signals are grouped roughly on the other side of the circular
genome, and often in vectors the small SV40 DNA fragment that is used may
contain both signals. You should also remember that polyadenylation requires
normally not only the AATAAA signal but also the polyadenylation acceptor
site (usually CA) 15-30 nucleotides downstream from the signal, which is
often followed by a G/T rich region. I have one vector which uses the early
SV40 polyadenylation signal and acceptor site. The late AATAAA signal is also
in the fragment, but at the very end, so it no longer has its acceptor site.
I have some evidence to back up the idea that this signal is not effective.
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