Transcription by RNA polymerase can stimulate localized
DNA supercoiling in
Escherichia coli.
In vivo, there is extensive
experimental support for a "twin-domain" model in which positive
DNA supercoils are generated ahead of a translocating RNA polymerase
complex and negative supercoils are formed behind it. Negative
supercoils accumulate in the template
DNA because the positive
supercoils are preferentially removed by cellular topoisomerase
action. Yet,
in vitro, clear and convincing support for the twin-domain
mechanism has been lacking. In this article, we reconcile this
inconsistency by showing that, in a defined
in vitro system with
plasmid
DNA templates, a variety of sequence-specific
DNA-binding
proteins, such as the bacteriophage

O replication initiator
or the
E. coli lactose or galactose repressors, strikingly stimulate
transcription-coupled
DNA supercoiling. We demonstrate further
that this stimulation requires the presence in the
DNA template
of a recognition sequence for the relevant
DNA-binding protein
and depends on the production of long RNA chains by an RNA polymerase.
Our data are most consistent with a model in which specific
DNA-binding
proteins facilitate a twin-domain mechanism to enhance
DNA supercoiling during transcription. More precisely, we suggest that some nucleoprotein
complexes, perhaps those that contain sharply bent
DNA, can form
barriers that impede the diffusion and merger of independent chromosomal
supercoil domains. Localization of
DNA supercoils by nucleoprotein
complexes may serve as a general mechanism for modulating
DNA transactions that are sensitive to
DNA superhelicity.
http://www.pnas.org/cgi/content/abstract/99/14/9139
2 comments:
Thanks for your comment on my blog.I just popped over to your blog and I think I will spend hours reading all of these which sounds alien to a crafter!!!
TC
Hey thank you for stopping by! :-) Just as tassycrafty said, I will spend some good time reading this :-) I WILL FOR REAL!
Michael
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