SPO11 dimers are sufficient to catalyse DNA double-strand breaks in vitro.

SPO11 initiates meiotic recombination through the induction of programmed DNA double-strand breaks (DSBs), but this catalytic activity has never been reconstituted in vitro. Here, using Mus musculus SPO11, we report a biochemical system that recapitulates all the hallmarks of meiotic DSB formation. We show that SPO11 catalyses break formation in the absence of any partners and remains covalently attached to the 5' broken strands.

Structural insight into Tn3 family transposition mechanism.

Transposons are diverse mobile genetic elements that play the critical role as genome architects in all domains of life. Tn3 is a widespread family and among the first identified bacterial transposons famed for their contribution to the dissemination of antibiotic resistance. Transposition within this family is mediated by a large TnpA transposase, which facilitates both transposition and target immunity.

DNA-driven condensation assembles the meiotic DNA break machinery.

The accurate segregation of chromosomes during meiosis-which is critical for genome stability across sexual cycles-relies on homologous recombination initiated by DNA double-strand breaks (DSBs) made by the Spo11 protein. The formation of DSBs is regulated and tied to the elaboration of large-scale chromosome structures, but the protein assemblies that execute and control DNA breakage are poorly understood. Here we address this through the molecular characterization of Saccharomyces cerevisiae RMM (Rec114, Mei4 and Mer2) proteins-essential, conserved components of the DSB machinery.

Unlocking Tn3-family transposase activity in vitro unveils an asymetric pathway for transposome assembly.

The Tn3 family is a widespread group of replicative transposons that are notorious for their contribution to the dissemination of antibiotic resistance and the emergence of multiresistant pathogens worldwide. The TnpA transposase of these elements catalyzes DNA breakage and rejoining reactions required for transposition. It also is responsible for target immunity, a phenomenon that prevents multiple insertions of the transposon into the same genomic region.

The Tn3-family of Replicative Transposons.

Transposons of the Tn3 family form a widespread and remarkably homogeneous group of bacterial transposable elements in terms of transposition functions and an extremely versatile system for mediating gene reassortment and genomic plasticity owing to their modular organization. They have made major contributions to antimicrobial drug resistance dissemination or to endowing environmental bacteria with novel catabolic capacities. Here, we discuss the dynamic aspects inherent to the diversity and mosaic structure of Tn3-family transposons and their derivatives.

Separate structural and functional domains of Tn4430 transposase contribute to target immunity.

Like other transposons of the Tn3 family, Tn4430 exhibits target immunity, a process that prevents multiple insertions of the transposon into the same DNA molecule. Immunity is conferred by the terminal inverted repeats of the transposon and is specific to each element of the family, indicating that the transposase TnpA is directly involved in the process.However, the molecular mechanism whereby this protein promotes efficient transposition into permissive targets while preventing transposition into immune targets remains unknown.