On page 789, Jarrell and colleagues devise a method for joining DNA fragments without first digesting them with restriction enzymes. To generate single-stranded RNA or DNA overhangs, they primed polymerase chain reactions with oligonucleotides that contain regions of RNA that cannot be copied by certain DNA polymerases. This created sticky-ended DNA fragments that could be ligated together, and then the RNA portions converted into DNA by a polymerase that can copy RNA. Besides eliminating the need for restriction enzymes, the method allows complete control over the composition and length of the 5′ overhang.