SMALL RNA ACTS AS AN ANTISILENCER OF THE H-NS-SILENCED RCSA GENE OF ESCHERICHIA-COLI

The regulation of capsular polysaccharide synthesis in Escherichia col i K-12 depends on the level of an unstable positive regulator, RcsA. T he amount of RcsA protein is limited both by its rapid degradation by Lon, an ATP-dependent protease, and by its low level of synthesis. We have found that the low level of expression from the rcsA promoter is due to transcriptional silencing by the histone-like protein H-NS; thi s silencing is sensitive to both sequence and context in a region upst ream of the -35 region of the promoter. A small (85-nt) RNA, DsrA, whe n overproduced, activates transcription of rcsA::lacZ fusions by count eracting H-NS silencing. DsrA RNA does not show any extended homology with the rcsA promoter or other sequenced regions of E. coli. Since th e stimulation of rcsA transcription by this small RNA does not depend on any sequences from within the rcsA transcript, DsrA acts, either di rectly or indirectly, on rcsA transcription initiation.