run-off transcription

[Sean Rollins]

I've read several times that it is preferable to linearize my vector for T7 in 
vitro transcription with a UNIQUE restriction site.  Does this mean the entire 
plasmid should have only one of the required sites (to terminate the 
transcript)? Or does this mean to make sure that your desired transcript 
sequence does not contain this site?  If the entire plasmid should have only 
one of the linearization sites, why is this necessary?  Do extraneous 
linear DNA fragments somehow inhibit T7 pol from recognizing the T7 promoter? 
 Any advice would be greatly appreciated.
				Thank you
				Sean Rollins
				Rollins.24 at osu.edu