Help! Questions about transcriptional elements in SV40 'control' region

[David P. Frazier]

In article <3qlnaj$ojr at nntp3.u.washington.edu>, aurelia at u.washington.edu
(A. M. Lotto) wrote:

> <-- early   tata       21 bp repeats            72 bp segments
> ____________________________________________________________________________
>    |        XXXX  |  21  |  21  | 21  | |     72       |     72       |
> ----------------------------------------------------------------------------
>       Ori                                                       late -->
> 
> 
> My questions regard the sequence of events.  Enhancers bind to TFIID.  
> SP1 binds to GC boxes in 21 bp repeat sequences.  TFIID interacts with 
> SP1 and SP1 interacts with RNA Pol II which doesn't know where to bind 
> the DNA.  First, I am not entirely sure the previous sequence of events 
> is even close to correct, secondly, how do these components interact to 
> increase the efficiency of txn?  Where does TFIID bind?  My sources say 
> that the enhancers bind to the 72 bp sequences but also that TFIID binds 
> enhancers.   I am confused about this and would greatly appreciate anyone 
> able to shed some light on these interactions.
> 
Amy, 
I don't want to get into doing your homework or take-home final exam for you,
but your awesome drawing of the SV40 control region fished me in.  The key
point for you to consider is that DNA is a yarn, not a stick.  This allows
the promoter regions to bend into loops such that proteins that bind to
the 72 bp sequence can interact with proteins that bind to the TATA
region.  My other 
hint is that TFIID is a general transcription factor that binds to a region 
common to many eukaryotic promoters.
I hope this helps, but not too much.

David Frazier
Department of Microbiology and Molecular Genetics
Harvard Medical School