ZIP1-INDUCED CHANGES IN SYNAPTONEMAL COMPLEX STRUCTURE AND POLYCOMPLEX ASSEMBLY

The yeast Zip1 protein is a component of the synaptonemal complex (SC) , which is an elaborate macromolecular structure found along the lengt hs of chromosomes during meiosis. Mutations that increase the length o f the predicted coiled. coil region of the Zip1 protein show that Zip1 influences the width of the SC. Overexpression of the ZIP1 gene resul ts in the formation of two distinct types of higher order structures t hat are found in the nucleus, but not associated with chromatin. One o f these structures resembles the polycomplexes that have been observed in many organisms and are thought to be aggregates of SC components. The second type of structure, which we have termed ''networks:'' does not resemble any previously identified SC-related structure. Assembly of both polycomplexes and networks can occur independently of the Hop1 or Red1 protein, which are thought to be SC components. Our results d emonstrate that Zip1 is a structural component of the central region o f the SC. More specifically, we speculate that Zip1 is a component of the transverse filaments that lie perpendicular to the long axis of th e complex.