Summary Homologous recombination (HR) is essential for high-fidelity DNA repair during mitotic proliferation and meiosis. Yet, context-specific modifications must tailor the recombination machinery to avoid (mitosis) or enforce (meiosis) the formation of reciprocal exchanges—crossovers—between recombining chromosomes. To obtain molecular insight into how crossover control is achieved, we affinity purified 7 DNA-processing enzymes that channel HR intermediates into crossovers or noncrossovers from vegetative cells or cells undergoing meiosis. Using mass spectrometry, we provide a global characterization of their composition and reveal mitosis- and meiosis-specific modules in the interaction networks. Functional analyses of meiosis-specific interactors of MutLγ-Exo1 identified Rtk1, Caf120, and Chd1 as regulators of crossing-over. Chd1, which transiently associates with Exo1 at the prophase-to-metaphase I transition, enables the formation of MutLγ-dependent crossovers through its conserved ability to bind and displace nucleosomes. Thus, rewiring of the HR network, coupled to chromatin remodeling, promotes context-specific control of the recombination outcome.

Recent advances inde novoprotein design have delivered a diversity of discretede novoprotein structures and complexes. A new challenge for the field is to use these designs directly in cells to intervene in biological process and augment natural systems. The bottom-up design of self-assembled objects like microcompartments and membraneless organelles is one such challenge, which also presents opportunities for chemical and synthetic biology. Here, we describe the design of genetically encoded polypeptides that form membraneless organelles inEscherichia coli(E. coli). To do this, we combinede novoα-helical sequences, intrinsically disordered linkers, and client proteins in single-polypeptide constructs. We tailor the properties of the helical regions to shift protein assembly from diffusion-limited assemblies to dynamic condensates. The designs are characterised in cells andin vitrousing biophysical and soft-matter physics methods. Finally, we use the designed polypeptide to co-compartmentalise a functional enzyme pair inE. coli.