HELP nuclear runon nuclear runoff

Rick Nicholson R.Nicholson at
Tue Aug 27 22:08:19 EST 1996

Anis Limami wrote > I would like that somebody explain me the difference
> the two methods Nuclear run-off and nuclear run-on.
> I looked in recipe books (current methods in M. B.) I found 
> only runoff.

	Historically nuclear run-on referred to the extension in-vitro of
transcripts initiated in-vivo.  That is the nuclei are isolated and the
RNA molecules which had begun to be synthesised in-vivo are extended, or
run-on, in-vitro.  
	The term run-off transcription (coined by Kreig and Melton around 1984
in NAR, and Meth. Enzymol 1988) referred to in-vitro transcription from
linearized DNA template.  Hence the term run-off, as the polymerase ran
until it fell off the template.  (The traditional run-off procedures are
described in manuals such as the Promega Protocols and Applications
	Somehow during the past decade many people have started using the term
nuclear run-off rather than run-on.  Although run-on is a more accurate
term, it seems to have become acceptable to also call it nuclear
Richard C. Nicholson, BSc PhD
Senior Research Fellow
Centre for Immunology
St. Vincent's Hospital
Sydney, Australia 2010

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