Improved Methods for Preparing the Telomere Tethering Complex Bqt1-Bqt2 for Structural Studies

In eukaryotes, chromosome ends (telomeres) are tethered to the inner nuclear membrane. During the early stages of meiosis, telomeres move along the nuclear membrane and gather near the spindle-pole body, resulting in a bouquet-like arrangement of chromosomes. This chromosomal configuration appears to be widely conserved among eukaryotes, and is assumed to play an important role in the normal progression of meiosis, by mediating the proper pairing of homologous chromosomes. In fission yeast, the Bqt1-Bqt2 protein complex plays a key role in tethering the telomere to the inner nuclear membrane. However, the structural details of the complex required to clarify how telomeres are gathered near the spindle-pole body remain enigmatic. Previously, we devised a preparation procedure for the Schizosaccharomyces japonicus Bqt1-Bqt2 complex, in which a SUMO tag was fused to the N-terminus of the Bqt1 protein. This allowed us to purify the Bqt1-Bqt2 complex from the soluble fraction. In the present study, we found that a maltose-binding protein homolog, Athe_0614, served as a better fusion partner than the SUMO protein, resulting in the marked increase in the solubility of the Bqt1-Bqt2 complex. The Athe_0614 fusion partner may open up new avenues for X-ray crystallographic analyses of the structure of the Bqt1-Bqt2 complex.