U6, H1 siRNA - (Dec/11/2006 )

hi I have a question about shRNA promoter
what is the difference between H1 and U6.
is the polyT added sequence in 3' of the oligo are specific for H1 or U6?
thanks
jm

poly T sequences after either H1 U6 or 7SK are terminal signals for the polymerase III transcription machinery.
Both promoters you've cited are efficient for siRNA transcription.