Bacterial RecA plays a central role in DNA repair and regulation of the SOS response to DNA damage, and has been suggested as a new antibiotic drug target. To develop a new tool to study RecA function, we engineered artificial small RNAs (sRNAs) that can posttranscriptionally repress RecA expression in Escherichia coli. The artificial sRNAs mimic the bacterial noncoding sRNAs which possess an antisense domain that is partially complementary to the targeted mRNA. We screened a library of artificial sRNAs with a randomized antisense domain and isolated several anti-recA sRNAs that can knockdown the endogenous RecA level in E. coli. The cells expressing the anti-recA sRNAs were found to exhibit phenotypes consistent with RecA repression such as reduced swarming motility and increased susceptibility to ciprofloxacin, a fluoroquinone antibiotic. (C) 2012 Elsevier Inc. All rights reserved.