HELP nuclear runon nuclear runoff

[Rick Nicholson]

Anis Limami wrote > I would like that somebody explain me the difference
between 
> 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
guide.) 
	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
run-off.  
	
-- 
Richard C. Nicholson, BSc PhD
Senior Research Fellow
Centre for Immunology
St. Vincent's Hospital
Sydney, Australia 2010