890475.fig.001
Figure 1: Schematic overview of nonhomologous centromere (CEN) coupling and synaptonemal complex (SC) formation in budding yeast meiotic prophase. Stable binding of Zip1 to the CENs in Rec8-dependent manner leads to nonhomologous CEN coupling in early meiotic prophase (1, 2) [57]. CEN coupling is regulated by the phosphorylation-state of Zip1 owing to Mec1 kinase and PP4 phosphatase activities [8]. Spo11- catalyzed DNA DSBs (red arrows in 3) trigger Mec1 activity leading to Zip1-phosphorylation and uncoupling of the nonhomologous CENs (4). DSB-induced crossover recombination (red arrows in 4, 5) initiates formation of the central element (CE) of SC between the homologous chromosomes (5). Though Mec1 and PP4 activities are likely in equilibrium in presence of DNA DSBs, Mec1- catalyzed uncoupling of the nonhomologous CENs is shown here as the driven direction (thick arrow linking 3 and 4) since, in wild-type meiosis, recombination and subsequent SC formation between the homologous chromosomes stabilize and sequester the homologous CENs from cycle of coupling-uncoupling [5, 8]. Two pairs of homologous chromosomes (black and blue) are shown. For simplicity, only one chromatid per chromosome is shown. Lateral elements of SC and Rec8 on chromosome arms are not shown. Chromosome ends are clustered and attached to the nuclear membrane.