I have a phenotype, but northern says gene is not knocked down - rnai knockdown (Apr/03/2005 )

I have recevied a line that is an rnai knockdown (supposedly) of a histone gene. I am getting a phenotype from this line that is segregating with the construct, however my northern analysis tells me that the endogenous gene is expressing rna just fine and is therefore not knocked down. I do not think the generic construct is causing the phenotype, since construct controls without the rnai sequence do not exhibit the phenotype.

How can I get rna expression but still have a phenotype? Should I do a western?

Thanks.

hi
definitely do a western blot.
but you can also do in a parallel experiment a northern to see the presence of your siRNA.