Figure 4.

Nuclear protein binding at the sns sites. The HpaII–Sau3A fragment (Fig. 1) was 3′ end labeled with [α-³²P]dATP and the large fragment of DNA polymerase I. The probe (1.5 ng) was incubated with 5 μg of nuclear extract from gastrula embryos in the absence or in the presence of 25, 50, and 100 ng of unlabeled homologous and plasmid fragments, respectively. Nuclear protein complexes were fractionated by acrylamide gel electrophoresis.