Single-molecule observation of DNA compaction by meiotic protein SYCP3.

In a previous paper (Syrjänen et al., 2014), we reported the first structural characterisation of a synaptonemal complex (SC) protein, SYCP3, which led us to propose a model for its role in chromosome compaction during meiosis. As a component of the SC lateral element, SYCP3 has a critical role in defining the specific chromosome architecture required for correct meiotic progression. In the model, the reported compaction of chromosomal DNA caused by SYCP3 would result from its ability to bridge distant sites on a DNA molecule with the DNA-binding domains located at each end of its strut-like structure. Here, we describe a single-molecule assay based on optical tweezers, fluorescence microscopy and microfluidics that, in combination with bulk biochemical data, provides direct visual evidence for our proposed mechanism of SYCP3-mediated chromosome organisation.