Mapping of the mucE transcriptional start site in P. aeruginosa PAO1. A) Primer extension mapping of mRNA 5′ end. Total RNA was isolated from the non-mucoid PAO1. The conditions used for labelling of primers for mucE are described in Methods. The primer extension product was run adjacent to the sequencing ladder generated with the same primer as highlighted in the mucE sequence. The arrow indicates the position of the P1 transcriptional start site of mucE. B) The mucE promoter sequence in strains PAO1 and PAO1VE2. The transposon (Tn) insertion site of PAO1VE2 is underlined along with the putative ribosome binding site (RBS) for mucE. In strain PAO1VE2, the gentamicin resistance cassette (aacC1) gene carries a σ70 dependent promoter. The arrow pointing leftward corresponds to the position of primer seq 1 used for mapping the P1 start site.