Selective binding of meiosis-specific yeast Hop1 protein to the holliday junctions distorts the DNA structure and its implications for junction migration and resolution.

Saccharomyces cerevisiae HOP1, which encodes a component of synaptonemal complex (SC), plays an important role in both gene conversion and crossing over between homologs, as well as enforces meiotic recombination checkpoint control over the progression of recombination intermediates. In hop1Delta mutants, meiosis-specific double-strand breaks (DSBs) are reduced to 10% of the wild-type level, and at aberrantly late times, these DSBs are processed into inter-sister recombination intermediates. However, the underlying mechanism by which Hop1 protein regulates these nuclear events remains obscure. Here we show that Hop1 protein interacts selectively with the Holliday junction, changes its global conformation and blocks the dissolution of the junction by a RecQ helicase. The Holliday junction-Hop1 protein complexes are significantly more stable at higher ionic strengths and molar excess of unlabeled competitor DNA than complexes containing other recombination intermediates. Structural analysis of the Holliday junction using 2-aminopurine fluorescence emission, DNase I footprinting and KMnO4 probing provide compelling evidence that Hop1 protein binding induces significant distortion at the center of the Holliday junction. We propose that Hop1 protein might coordinate the physical monitoring of meiotic recombination intermediates with the process of branch migration of Holliday junction.