Cover photograph: Genomic regions associated with differential expression from a library of promoter-reporter plasmids, which was generated by the method RAIL (rapid arbitrary PCR insertion libraries). (Image courtesy of Douglas B. Rusch, Indiana University, Bloomington.) (See related article in June 2018, vol. 200, no. 11, e00724–17.) (Copyright © 2018 American Society for Microbiology. All Rights Reserved.)