in vitro transcription - transcription of long transcripts (Jan/25/2007 )

hi to all
I'm trying to in vitro transcribe a long mRNA of about 8 kb.
does any one have suggestions or advices?
how to improve the transcription to the full length of RNA?
what kit or home made kit can I use?
how to purify the RNA product?
I will be greatfull for any help.
thanks
keren

there are a few kits on the market specific to purifying longer RNAs...I would try Invitrogen or Ambion

as far as tips to purify - be careful. you don't want to break or shear the RNA. even though 8kb isn't really that long...I would treat it like a chromosomal DNA prep