The ability of bacteria to acquire and disseminate heterologous genes has been a major factor in the development of multiple drug resistance. A gene, intl4, was identified that encodes a previously unknown integrase that is associated with a "gene-VCR" organization (VCRs are Vibrio cholerae repeated sequences), similar to that of the well-characterized antibiotic resistance integrons, The similarity was confirmed by Intl1-mediated recombination of a gene-VCR cassette into a class 1 integron. VCR cassettes are found in a number of Vibrio species including a strain of V. metschnikovii isolated in 1888, suggesting that this mechanism of heterologous gene acquisition predated the antibiotic era.