Six sbc::Tn5 insertions and one sbc::IS50 insertion, which cause recE expression in Escherichia coli, have been cloned, and their DNA sequences have been determined. The sites of insertion are found at three positions in a 10-bp region: 58, 63, and 68 bp upstream of recE. Primer extension experiments with the cloned Tn5 insertions demonstrate that recE transcripts start adjacent to the insertion elements of five of these mutations and both adjacent and one nucleotide within the insertion element for the sixth mutation. This supports the hypothesis that these mutations have inserted a promoter, and PCR analysis reveals an outward promoter within the distal 69 nucleotides of Tn5. Primer extension analysis of RNA from the uncloned Tn5 and IS50 mutants reveals three additional insertion sites close to the others. Because all the insertions lie in the spacer region between racC and recE, transcribed in sbcA6 and sbc-23 strains, we propose that these insertions be renamed recEs::Tn5 and recEs::IS50.