Disruption of any of these components leads to failure of telomere clustering and defective spore formation in meiosis. To ensure telomere attachment to the SPB, telomeres must be tethered to the nuclear envelope via the interaction between Rap1 and the inner nuclear membrane complex Bqt3 and Bqt4. Bouquet formation is achieved by expression of a pair of meiosis-specific proteins, Bqt1 and Bqt2, which bridge the telomeric proteins Taz1 and Rap1 to the SPB component Sad1. This period is also known as the ‘horsetail nucleus’ stage, during which the nucleus elongates and oscillates back and forth between the cell poles, following the spindle pole body or SPB (the yeast equivalent of the centrosome) driven by cytoplasmic microtubules. In fission yeast Schizosaccharomyces pombe, the telomere bouquet is observed throughout meiotic prophase. Recent studies suggest that the bouquet also plays a crucial role in meiotic spindle formation. This conserved reorganization of chromosomes during meiotic prophase has been observed in most eukaryotic organisms and is shown to promote homolog pairing and meiotic recombination. During meiotic prophase, the position of chromosomes within the nucleus is dramatically reorganized and telomeres cluster within a limited area of the nuclear envelope to form the so-called telomere bouquet. While telomeres are mostly known for their essential function in chromosome maintenance, they also play an important role in meiotic progression. Telomeres are specialized nucleoprotein structures that form the natural ends of linear chromosomes. Thus, Rap1 is able to retain bouquet formation under heavily phosphorylated status. Whereas Rap1 hyper-phosphorylation observed in meiotic prophase does not have an apparent role in bouquet formation, the intrinsic negative charge of Rap1 is important for forming interactions with its binding partners. Interestingly, mutations that change the charge of negatively charged residues within the Bqt1-2 binding site of Rap1 abolished the affinity to the Bqt1-2 complex, suggesting that the intrinsic negative charge of Rap1 is crucial for telomere bouquet formation. Despite the negative charge conferred by its highly phosphorylated state, Rap1 maintains interactions with its binding partners. Concomitant phosphomimetic mutation of the modification sites suggests that Rap1 hyper-phosphorylation does not directly regulate telomere bouquet formation or dissociation. Here, we detected high levels of Rap1 phospho-modification throughout meiotic prophase, and identified a maximum of 35 phosphorylation sites. Although it is known that this polarized chromosomal arrangement plays a crucial role in meiotic progression, the molecular mechanisms of telomere bouquet regulation are poorly understood. During meiotic prophase, the meiotic proteins Bqt1-2 bind Rap1 and tether to the spindle pole body to form the bouquet. In fission yeast, telomeres localize to the nuclear periphery via interaction of the telomeric protein Rap1 with the membrane protein Bqt4. Chromosomes reorganize in early meiotic prophase to form the so-called telomere bouquet.

Pearson protein scaffold chromosome