The essential function of meiosis is to haploidize the genome, a process which depends on chromosome pairing in meiotic prophase. A long history of cytological and genetic studies have suggested a role for telomere-mediated movements in meiotic chromosome pairing but there has been little experimental evidence for the role and few insights into the molecular mechanisms involved. The meiotic telomere protein Ndj1p is required for normal telomere organization and for normal meiotic chromosome behavior in S. cerevisiae, its absence causing delays-in axial element formation, synapsis and entry into the first meiotic division-and defects in chromosome recombination and segregation. Thus, Ndj1p may function at telomeres to facilitate chromosome pairing, perhaps at the early meiotic stage of bouquet formation. The hypothesis that Ndj1p fosters telomere-mediated homologous pairing by moving chromosomes together and/or by stabilizing pairing interactions will be tested by examining telomere positions in fixed, embedded material using a quantitative immunocytological approach and also by analyzing the movements of green fluorescent protein-tagged chromosomes in vivo. In addition, axial element formation, synapsis, and recombination will be compared in wild-type and NDJj1 deletion cells using a quantitative immunocytological approach, with particular attention to the kinetics of these events with respect to subnuclear locations. The hypothesis that NdJ1 is required for subtelomeric pairing associations that persist in the absence of recombination will be tested by assessing pairing near the telomeres using an in situ hybridization-based assay. The hypothesis that NDJ1 influences recombination by affecting DNA double-strand break formation will be assessed by comparing the frequency and positions of double-strand breaks and the kinetics of break formation in different wild-type backgrounds and in mutant backgrounds where breaks persist and are stable. Finally, essential genes which are candidates for interaction with NDJ1 will be evaluated for meiosis-and NDJ1-specific function using a plasmid-shuffle approach to identify separation-of-function and /or conditional mutations. The questions addressed by these experiments are of general significance for their importance in understanding mechanisms of meiotic chromosome pairing and of telomere-mediated positioning of chromosomes in the nucleus, which can influence any process sensitive to nuclear architecture, and thus affect the fidelity of chromosome segregation.
