RECA-LIKE PROTEINS ARE COMPONENTS OF EARLY MEIOTIC NODULES IN LILY

Early meiotic nodules (also called recombination nodules) are proteina ceous structures about 100 nm in diameter that are associated with for ming synaptonemal complexes (SCs) during early prophase I of meiosis. Although their function is unknown, early nodules may he involved in s earching for DNA homology before synaptic initiation, Two potential co mponents of early nodules are Rad51 and Dmc1 proteins, These proteins are important for meiotic recombination In eukaryotes and are homologo us to RecA, the major protein that catalyzes homologous pairing and DN A strand exchange in prokaryotes. In addition, Rad51 has been localize d by immunofluorescence in abundant foci that may correspond to early nodules in yeast, lily, and mouse, In yeast and lily, Dmc1 and Lim15, the lily homolog of Dmc1, colocalize with Rad51. Here, using electron microscopic immunogold localization to spreads of zygotene and early p achytene SCs from lily, we confirm that REcA-like proteins are compone nts of early nodules. The antibody used was generated to full-length t omato Rad51 protein and binds to both Rad51 and Lim15 in immunoblots o f lily primary microsporocyte proteins. The labeled early nodules are heterogeneous in size and are associated with both axial elements and SCs. There are two classes of early nodules, those that are densely la beled with gold and those that are not labeled at all. This result may he due to technical limitations associated with using spread preparat ions or to differences in the nodules themselves. The presence of Rad5 1 and/or Lim15 proteins in early nodules supports the hypothesis that early nodules are involved in recombination-related events during meio sis.