Proposed secondary structures of representative VXRs. Secondary structures and free energies were determined using the MFOLD (Walter et al. 1994) online interface at l'Institut Pasteur. The protruding C region of the proposed 2L site within the stem is boxed in VMeR 372-1, as are the nucleotides adjacent to the ICS and CS that are absolutely conserved in all 219 VXRs examined. A:T and G:C base pairs are marked with dark gray dots, respectively. (VCR) V. cholerae repeats; (VMeR) V. metschnikovii repeats; (VFR) V. fischerirepeats.