GENETIC INTERACTIONS BETWEEN HOP1, RED1 AND MEK1 SUGGEST THAT MEK1 REGULATES ASSEMBLY OF AXIAL ELEMENT COMPONENTS DURING MEIOSIS IN THE YEAST SACCHAROMYCES-CEREVISIAE

During meiosis, axial elements are generated by the condensation of si ster chromatids along a protein core as precursors to the formation of the synaptonemal complex (SC). Functional axial elements are essentia l for wild-type levels of recombination and proper reductional segrega tion at meiosis I. Genetic and cytological data suggest that three mei osis-specific genes, HOP1, RED1 and MEK1, are involved in axial elemen t formation in the yeast Saccharomyces cerevisiae. HOP1 and RED1 encod e structural components of axial elements while MEK1 encodes a putativ e protein kinase. Using a partially functional allele of MEK1, new gen etic interactions have been found between HOP1, RED1 and MEK1. Overexp ression of HOP1 partially suppresses the spore inviability and recombi nation defects of mek1-974; in contrast, overexpression of RED1 exacer bates the mek1-974 spore inviability. Co-overexpression of HOP1 and RE D1 in mek1-974 diploids alleviates the negative effect of overexpressi ng RED1 alone. Red1p/Red1p as well as Hop1p/Red1p interactions have be en reconstituted in two hybrid experiments. Our results suggest a mode l whereby Mek1 kinase activity controls axial element assembly by regu lating the affinity with which Hop1p and Red1p interact with each othe r.