Fig. 6. Gel shift analysis of the (GTTT)₄ sequence. (A) Incubation of an ³²P-labeled oligo containing the (GTTT)₄ sequence with Drosophila embryonic extracts causes the formation of several complexes (arrows). Most of these complexes can be competed by excess cold probe (lane 2), but not by the mutant probe (lane 3). Complexes are not formed with the mutant probe (lane 4). (B) Slp1 protein binds specifically to the (GTTT)₄ repeat. Increasing concentrations of a bacterial extract containing full-length Slp1 protein (lanes 4-6) causes formation of a specific complex (arrow). Binding can be competed by excess cold probe (lane 7), but not by the mutant probe (lane 8).