Figure 1.

Construction of the vectors pW-bc and pE3SP-bc. Part of the pW ribosomal minigene was PCR amplified in two steps. First, two fragments were generated using primers P1 and P2, or P3 and P4, respectively. Second, both fragments were joined by PCR with primers P1 and P4. The restriction sites PstI and EcoRI, introduced through PCR primers P1 and P4, were used to insert the resulting fragment into the pW and pE3SP (pE) vector backbones. P, mouse Pol I promoter; Tx, transcription termination signal; bc, basic construct; E, enhancer.