TRANSCRIPTION OF THE ESCHERICHIA-COLI RECE GENE FROM A PROMOTER IN TN5 AND IS50

Six sbc::Tn5 insertions and one sbc:IS50 insertion, which cause recE e xpression in Escherichia coli, have been cloned, and their DNA sequenc es have been determined. The sites of insertion are found at three pos itions in a 10-bp region: 58, 63, and 68 bp upstream of recE. Primer e xtension experiments with the cloned Tn5 insertions demonstrate that r ecE transcripts start adjacent to the insertion elements of five of th ese mutations and both adjacent and one nucleotide within the insertio n element for the sixth mutation. This supports the hypothesis that th ese mutations have inserted a promoter, and PCR analysis reveals an ou tward promoter within the distal 69 nucleotides of Tn5. Primer extensi on analysis of RNA from the uncloned Tn5 and IS50 mutants reveals thre e additional insertion sites dose to the others. Because all the inser tions lie in the spacer region between racC and recE, transcribed in s bcA6 and sbc-23 strains, we propose that these insertions be renamed r ecEs::Tn5 and recEs::IS50.