Transcription Dynamically Patterns the Meiotic Chromosome-Axis Interface [ChIP-chip]

Meiotic chromosomes are highly compacted yet remain transcriptionally active. To understand how chromosome folding accommodates transcription, we investigated the assembly of the axial element, the proteinaceous structure that compacts meiotic chromosomes and promotes recombination and fertility. We found that the axial-element proteins of budding yeast are flexibly anchored to chromatin by the ring-like cohesin complex and biased towards small chromosomes by a separate modulating mechanism that requires the conserved axial element component Hop1. The ubiquitous presence of cohesin at sites of convergent transcription provides well-dispersed points for axis attachment and thus compaction. Axis protein enrichment at these sites directly correlates with the propensity for recombination initiation nearby. Importantly, axis anchoring by cohesin is adjustable and readily displaced in the direction of transcription by the transcriptional machinery. We propose that such robust but flexible tethering allows the highly structured axial element to promote recombination while easily adapting to changes in chromosome activity. Two types of study were undertaken to understand the meiotic chromosomal axes assembly and its importance in DSB regulation in yeast. First, DSBs were mapped using ssDNA enrichment in strains isogenic for a dmc1 mutation, and also including rec8 deletion and pREC8-SCC1 in rec8 deletion. Second, the genome-wide distribution of meiotic or mitotic cohesin in meiosis was measured by ChIP-chip analysis in wild-type and pREC8-SCC1 in rec8 deletion.