Meiotic recombination between homologous chromosomes initiates via programmed DNA double-strand breaks (DSBs), generated by complexes comprising Spo11 transesterase plus accessory proteins. DSBs arise concomitantly with the development of axial chromosome structures, where the coalescence of axis sites produces linear arrays of chromatin loops. Recombining DNA sequences map to loops, but are ultimately tethered to the underlying axis. How and when such tethering occurs is currently unclear. Using ChIPchip in yeast, we show that Spo11-accessory proteins Rec114, Mer2, and Mei4 stably interact with chromosome axis sequences, upon phosphorylation of Mer2 by S phase Cdk. This axis tethering requires meiotic axis components (Red1/Hop1) and is modulated in a domain-specific fashion by cohesin. Loss of Rec114, Mer2, and Mei4 binding correlates with loss of DSBs. Our results strongly suggest that hotspot sequences become tethered to axis sites by the DSB machinery prior to DSB formation.

During meiotic prophase a number of important events require recombination between maternal and paternal chromosomes, which is initiated through the introduction of DNA double-strand breaks (DSBs). The majority of DSBs, which mostly occur at so-called hotspots, have been located between cohesin binding sites. qChIP (chromatin immunoprecipitation quantified by real-time PCR) is a sensitive, accurate, and cost-efficient alternative to ChIP-on-Chip for the analysis of noncovalent protein-DNA interactions at defined binding sites in vivo. Here we use qChIP to study Mre11 binding to three chromosomal loci during meiosis. We show that Mre11 interacts with a known hotspot region (UpsilonCR048) in the R-band of chromosome III, but not with a cold region in the G-band (UpsilonCR011). Interestingly Mre11 binds to a cohesin binding site (UpsilonCR067), 20 kb distal to UpsilonCR048, with similar intensity as to the hotspot, despite the absence of DSBs in this region.

Chromatin immunoprecipitation combined with massive parallel sequencing (ChIP-seq) is increasingly used to study protein-chromatin interactions or local epigenetic modifications at genome-wide scale. ChIP-seq can be performed directly with several ng of immunoprecipitated DNA, which is generally obtained from a several million cells, depending on the quality of the antibody. ChIP-seq can only provide binding/modification information for a single epitope but multidimensional analyses require often information about the coordinate binding of several factors to, and/or corresponding epigenetic modification of targets sites. To this aim sequential ChIP assays (reChIP) can in principle be combined with massive parallel sequencing but the low yields associated to such approach have seriously hampered widespread application. The present protocol couples a linear DNA amplification (LinDA) step to reChIP assays, thus facilitating global studies by using the LinDA-reChIP-seq protocol.