title: A Happy 3' Ending to the piRNA Maturation Story.
abstract: For a decade, mystery has surrounded the mechanisms by which piRNA biogenesis yields distinct size classes of small RNAs within individual PIWI proteins. In this issue of Cell, two studies shed light on this process, identifying conserved PARN-family exonucleases that trim piRNAs to their mature size in silkworms and C. elegans.
authors.affiliation: Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge, CB2 0RE, UK. Electronic address: benjamin.czech@cruk.cam.ac.uk.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Czech
authors.affiliation: Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge, CB2 0RE, UK. Electronic address: greg.hannon@cruk.cam.ac.uk.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Hannon