Schematic diagram of the constructs used for in vivo expression of IRNA. The diagram (not to scale) shows the cloning of IRNA encoding sequences into eukaryotic expression vector pCDNA3 (Invitrogen). The polylinker site following the cytomegalovirus (CMV) promoter sequence is illustrated above the parental plasmid. Additional construction of different IRNA-encoding plasmids are shown, and their names are given at the left. BGH, bovine growth hormone; pA, poly(A) site; SV40, simian virus 40; ori, origin.