ABC-leaders. (a) The ABC-leader found upstream of the potABCD operon, encoding a spermidine/putrescine import system, in the Gammaproteobacteria Haemophilus somnus and Pasteurella multocida. (b) The ABC-leader found in the lactobacilli Lactobacillus gasseri and Lactobacillus johnsonii, upstream of a multidrug export system operon. (c) The T-box found in the Firmicutes Enterococcus faecalis and Lactobacillus sakei, upstream of genes for metal ion and methionine transporters, respectively. (d) The ABC-leader found in bacilli upstream of an alkanesulfonates transporter operon. (e) The ABC-leader found in bacilli 15-nucleotides upstream of a transporter of unknown specificity. Candidates are represented using the same conventions as in Figure 3.