PubMed · 9925496
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R Sikorski, R Peters. 1999-01-15. Cloning 3.0?. https://doi.org/10.1126/science.283.5400.349a
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The Sinorhizobium meliloti lpsS gene encodes a sulfotransferase that modifies lipopolysaccharide. Mutants lacking lpsS display no defect in lipopolysaccharide sulfation when assayed under laboratory conditions, but exhibit an abnormal symbiosis with alfalfa. These results suggest that lpsS is transcriptionally repressed under laboratory conditions, but upregulated during symbiosis. Here, it is shown that lpsS, as well as exo genes required for the biosynthesis of succinoglycan, are transcriptionally repressed in laboratory media containing divalent cations. Furthermore, the divalent cation-dependent transcriptional downregulation of lpsS is dependent on the exoR gene, which encodes a global regulator of transcription.
The rpoZ gene for the omega subunit of Escherichia coli RNA polymerase constitutes single operon with the spoT gene, which is responsible for the maintenance of stringent response under nutrient starvation conditions. To identify the physiological role of the omega subunit, we compared the gene expression profile of wild-type Escherichia coli with that of an rpoZ deleted strain by microarray analysis using an E. coli DNA chip. Here we report on a set of genes which show changes in expression profile following the removal of rpoZ. We have seen that relA, which is responsible for the synthesis of the stringent factor ppGpp and many ribosomal proteins, exhibited noticeable changes in mRNA levels and were therefore further analyzed for their expression using a GFP/RFP two-fluorescent protein promoter assay vector. In the absence of rpoZ, the promoter for the relA gene was severely impaired, but the promoters from the ribosomal protein genes were not affected as much. Taking these results together we propose that the omega subunit is involved in regulation of the relA gene, but induction of the stringently controlled genes in the absence of rpoZ is, at least in part, attributable to a decrease in ppGpp level.
A cluster of six genes from Flavobacterium hibernum strain W22, fus-rpsJ-rplC-rplD-rplW-rplB, was cloned and sequenced. A short fragment upstream of rplC, but not of rpsJ, showed strong promoter activity in flavobacteria. TATCTTTG and TTG motifs that are conserved in Flavobacterium promoters were found immediately upstream of the transcription start point of rplC, at the -7 and -33 positions, respectively. RT-PCR analysis of the transcripts revealed that rpsJ and rplC are expressed as separate transcriptional units, whereas rplC and rplD-rplW-rplB are cotranscribed as a single mRNA, in contrast to the situation in the Gammaproteobacteria, which have a single transcriptional unit of 11 ribosomal S10 genes.