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PIWI-interacting RNAs (piRNA) suppress selfish genetic elements and are essential for germ cell biology in animals. They also play critical roles in regeneration in planaria, regulate gene expression in adult mammalian testes, and participate in antiviral defense in mosquitoes. Inspired by a recent workshop on PIWI proteins and piRNAs, this commentary aims to summarize fundamental aspects of piRNA biology, highlight recent advances, and discuss key outstanding questions. It is written by and for biochemists, geneticists, and evolutionary biologists, and represents our interdisciplinary perspective. This commentary highlights, from an interdisciplinary perspective, recent advances and key outstanding questions in the field of piRNA biology. [ABSTRACT FROM AUTHOR]

The crystal structure of the complex between the N-terminal DNA-binding domain of Tc3 transposase and an oligomer of transposon DNA has been determined. The specific DNA-binding domain contains three -helices, of which two form a helix­turn­helix (HTH) motif. The recognition of transposon DNA by the transposase is mediated through base-specific contacts and complementarity between protein and sequence-dependent deformations of the DNA. The HTH motif makes four base-specific contacts with the major groove, and the N-terminus makes three base-specific contacts with the minor groove. The DNA oligomer adopts a non-linear B-DNA conformation, made possible by a stretch of seven G:C base pairs at one end and a TATA sequence towards the other end. Extensive contacts (seven salt bridges and 16 hydrogen bonds) of the protein with the DNA backbone allow the protein to probe and recognize the sequence-dependent DNA deformation. The DNA-binding domain forms a dimer in the crystals. Each monomer binds a separate transposon end, implying that the dimer plays a role in synapsis, necessary for the simultaneous cleavage of both transposon termini. [ABSTRACT FROM AUTHOR]