Preliminary molecular replacement results for a crystalline gene 5 protein–deoxyoligonucleotide complex

Complexes of the gene 5 protein from bacteriophage fd with a variety of oligodeoxynucleotides, ranging in length from two to eight and comprised of several different sequences, have been formed and crystallized for X‐ray diffraction analysis. The crystallographic parameters of four different unit cells, all of which are based on hexagonal packing arrangements, indicate that the fundamental unit of the complex is composed of six gene 5 protein dimers. We believe this aggregate has 622 point group symmetry and is a ring formed by end‐to‐end closure of a linear array of six dimers. From our results we have proposed a double‐helix model for the gene 5 protein–DNA complex in which the protein forms a spindle or core around which the DNA is spooled. Currently 5.0‐Å X‐ray diffraction data from one of the crystalline complexes is being analyzed by molecular replacement techniques to obtain a direct image of the protein–nucleic acid complex.