DSRA RNA REGULATES TRANSLATION OF RPOS MESSAGE BY AN ANTI-ANTISENSE MECHANISM, INDEPENDENT OF ITS ACTION AS AN ANTISILENCER OF TRANSCRIPTION

DsrA RNA regulates both transcription, by overcoming transcriptional s ilencing by the nucleoid-associated H-NS protein, and translation, by promoting efficient translation of the stress a factor, RpoS. These tw o activities of DsrA can be separated by mutation: the first of three stem-loops of the 85 nucleotide RNA is necessary for RpoS translation but not for anti-H-NS action, while the second stem-loop is essential for antisilencing and less critical for RpoS translation. The third st em-loop, which behaves as a transcription terminator, can be substitut ed by the trp transcription terminator without loss of either DsrA fun ction. The sequence of the first stem-loop of DsrA is complementary wi th the upstream leader portion of rpoS messenger RNA, suggesting that pairing of DsrA with the rpoS message might be important for translati onal regulation. Mutations in the Rpos leader and compensating mutatio ns in DsrA confirm that this predicted pairing is necessary for DsrA s timulation of RpoS translation. We propose that DsrA pairing stimulate s RpoS translation by acting as an anti-antisense RNA, freeing the tra nslation initiation region from the cis-acting antisense RNA and allow ing increased translation.