Figure 2.

Testing the insulating activity of the core element. Six copies of the 250-bp fragment containing 5′HS4 (p179) or two copies of the fragment plus a 950-bp fragment from λ phage DNA (p176) were inserted between the LCR and the ^Aγ-neo reporter gene. The number of G418-resistant colonies was determined as in Fig. 1, and the number obtained for pJC5-4, which contains one copy of the intact insulator on both sides of the reporter gene, was set to 1.0.