title: Single-molecule DNA analysis reveals that yeast Hop1 protein promotes DNA folding and synapsis: implications for condensation of meiotic chromosomes.
abstract: During meiosis, long-range interaction between homologous chromosomes is thought to be crucial for homology recognition, exchange of DNA strands, and production of normal haploid gametes. However, little is known about the identity of the proteins involved and the actual molecular mechanism(s) by which chromosomes recognize and recombine with their appropriate homologous partners. Single-molecule analyses have the potential to provide insights into our understanding of this fascinating and long-standing question. Using atomic force microscopy and magnetic tweezers techniques, we discovered that Hop1 protein, a key structural component of  Saccharomyces cerevisiae  synaptonemal complex, exhibits the ability to bridge noncontiguous DNA segments into intramolecular stem-loop structures in which the DNA segments appear to be fully synapsed within the filamentous protein stems. Additional evidence suggests that Hop1 folds DNA into rigid protein-DNA filaments and higher-order nucleoprotein structures. Importantly, Hop1 promotes robust intra- and intermolecular synapsis between double-stranded DNA molecules, suggesting that juxtaposition of DNA sequences may assist in strand exchange between homologues by recombination-associated proteins. Finally, the evidence from ensemble experiments is consistent with the notion that Hop1 causes rigidification of DNA molecules. These results provide the first direct evidence for long-range protein-mediated DNA-DNA synapsis, independent of crossover recombination, which is presumed to occur during meiotic recombination.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Krishnendu
authors.initials: K
authors.lastname: Khan
authors.forename: Usha
authors.initials: U
authors.lastname: Karthikeyan
authors.forename: You
authors.initials: Y
authors.lastname: Li
authors.forename: Jie
authors.initials: J
authors.lastname: Yan
authors.forename: K
authors.initials: K
authors.lastname: Muniyappa
mesh_terms: D023902:Chromosome Pairing; D015825:Chromosomes, Fungal / Q000235:genetics*; D004271:DNA, Fungal / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003851:Deoxyribonucleases / Q000378:metabolism; D055029:Inverted Repeat Sequences; D009690:Nucleic Acid Conformation; D009698:Nucleoproteins / Q000737:chemistry / Q000378:metabolism; D055550:Protein Stability; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C086672:HOP1 protein, S cerevisiae; D009698:Nucleoproteins; D029701:Saccharomyces cerevisiae Proteins; D003851:Deoxyribonucleases