DNA binding by the bacteriophage SPO1-encoded type II DNA-binding protein, transcription factor 1. Formation of nested complexes at a selective binding site.

The interactions of the phage SPO1-encoded Type II DNA-binding protein, transcription factor 1 (TF1), with one of its preferred binding sites in SPO1 DNA have been analyzed in detail. The results suggest that TF1 recognizes a high-affinity "core" binding site and that additional protein moieties can accrue to either side of the occupied core site to form higher order complexes. Close contacts between TF1 and the core binding site as well as some of the steric requirements for recognition of the core site were determined. Comparison of the nucleotide sequences of several preferred binding sites for TF1 reveals a striking lack of precise homology but does show common features.