Total RNA was extracted from 1.5 ml culture samples by the 'Hot-phenol' extraction method and separated according to size by electrophoresis on 1.2% agarose, 6% formaldehyde gels in recirculating 1xMOPS buffer. Capillary blots were performed onto Hybond-N + (Perkin Elmer) membranes, and the RNA was crosslinked to the membrane by 0.12 J/cm2 UV light in a Stratalinker 1800. Riboprobes covering mRNA sequences as described in Figure 4 were made by T7 RNA polymerase transcripts from the pMAS39 'downstream' template (19) or from templates made by PCR where one primer included 'hanging out' T7 promoter sequences (gene10 and lacZ 5 0 probes). The riboprobes were synthesized in the presence of 32-P-UTP and the final specific activity was about 40 Ci/mmol of nucleotide. Hybridization and stripping of membranes were performed following standard protocols (Amersham, Hybond-N+ booklet, 2006). The membranes were wrapped in Saran wrap and placed on a phosphor imager screen (Molecular Dynamics) and left to expose over night. Signals were visualized using ImageQuant software.