Meiotic segregation, synapsis, and recombination checkpoint functions require physical interaction between the chromosomal proteins Red1p and Hop1p

In yeast, HOP1 and RED1 are required during meiosis for proper chromosome s egregation and the consequent formation of viable spores. Mutations in eith er HOP1 or RED1 create unique as well as overlapping phenotypes, indicating that the two proteins act alone as well as in concert with each other. To understand which meiotic processes specifically require Red1p-Hop1p hetero- oligomers, a novel genetic screen was used to identify a single-point mutat ion of RED1, red1-K318E, that separates Hop1p binding from Red1p homooligom erization. The Red1-K348E protein is stable, phosphorylated in a manner equ ivalent to Red1p, and undergoes efficient homo-oligomerization; however, it s ability to interact with Hop1p both by two-hybrid and coimmunoprecipitati on assays is greatly reduced. Overexpression of HOP1 specifically suppresse s red1-K348E, supporting the idea that the only defect in the protein is a reduced affinity for Hop1p, red1-K348E mutants exhibit reduced levels of cr ossing over and spore viability and fail to undergo chromosome synapsis, th ereby implicating a role for Red1p-Hop1p hetero-oligomers in these processe s. Furthermore, red1-K348E suppresses the sae2/com1 defects in meiotic prog ression and sporulation, indicating a previously unknown role for HOP1 in t he meiotic recombination checkpoint.