FIG. 2.

(a) Northern blot analysis of the mRNA transcript encompassing the espA, espD, and espB genes. Total RNA extracted from EDL933 grown on DMEM-HEPES was fractionated on a 1% agarose gel, transferred to Byodine B membranes, and hybridized with probes specific for espA, espD, and espB. As a control, a probe that hybridizes within regions located upstream of espA (sepL) was used. The main RNA transcript is indicated by an arrow (approximately 2.8 kb). (b) Identification of the transcriptional start site from the esp operon by primer extension analysis. Total RNA was extracted from EDL933(pUJ3) grown exponentially at 37°C in medium supplemented with either 10 (lane 1) or 430 (lane 2) mM NaCl. A 24-bp oligonucleotide (FAB56), which hybridizes with positions +3 to −21 of the espA region, was used to perform primer extension and to generate a sequence ladder. The position of the first base in the main RNA message relative to the adenosine (base +1) of the ATG start codon is indicated.